For me that's the Athlon TB 1400, as well as the AMD K5 and the Intel 286. The 286 was the one in my very first PC, and it was GREAT. The K5 was my first server, and the Athlon TB was the processor in the first PC I bought myself. The 286 was clocked well beyond specs, at a whopping 16 mhz 
My first OC'ed processor too!
hoi Thandor :w
I really like the 286-processor. Main reason is because it was the first PC 'we' had 
A picture of one of the most beautiful CPU's (LLC 80286's, at bottom. Two upside down, the other not.) :
Besides the 286 I like a few others. Which includes CPU's like the Intel 80486DX/2-66 with a blue heatsink. See the picture above in the back. The chip above the old-style 3Dfx Voodoo3 chip. And of course the AMD Athlon processor. More or less I like all the K7-based CPU's. The 'Classic' (Slot A) version impresses me the most 
I really like the Pentium Pro of the old days they always seemed to tha bomb heh but they always had a heavy price tag and my favorite CPU of today are the Opteron CPU's, they always served my systems well as such and they are rock solid as well as stability goes
Pentium !!! Coppermine 1Ghz CPU's are cool too nice for SMP setups of their time if the Xeon was too expensive, the P3/EB's were a very good alternative, my Dual P3/EB still works January 28 2009 it will turn 9 years old and still going on strong.
The AMD Opteron indeed goes like a rocket. My server is running two dual-core AMD Opteron 2218 engineering samples which were produced almost one year before the actual launch of the second-generation AMD Opteron's. I like the K7 Athlon CPU's and as the K8 is based upon the K7 design the K8 is cool, too .
A dual Intel Pentium !!! 'Coppermine' at 1GHz is a nice combo. Had one too for a while but the motherboard got stability issues after a while. This also reminds me I don't have AMD's first dual-CPU capable Athlon CPU which are probably both the ceramic AMD Athlon MP 1000MHz and 1200MHz 'Palomino' .
heh well all my systems now have a variety of CPU's hehe Retro to Mid Gen, not such a New Gen guy.
AMD AthlonXP 2700+ Thoroughbred-B 2167Mhz, 256KB L2 & 333Mhz FSB this one is used for the 3dfx test system, this one uses the most reliable and stable motherboard to test 3dfx prototypes including all 6 Voodoo5 6000 revisions, it's called the EPoX EP-8K3A+ Ver 1.1, it also has 3x 512MB PC 32-- CL2 Kingston Hyper X @ PC 2700 CL1.5 for great stability and somewhat better ram timings
Dual Intel Pentium!!!/EB 1.00Ghz Coppermine's 2x 998Mhz, 2x 256KB L2 & 133Mhz FSB, these are used for my emergency backup server, always a handy machine to have on standby.
Intel Pentium4-E 3400HT Prescott 3400Mhz, 1MB L2 & 800Mhz FSB [200mhz Quad Pumped] this one is used in my gaming laptop a Dell Inspiron 9100 Limited Xtreme Edition, a small run of 9100's with the hardware of the 9100 XPS a rare and short run, VGA is the Powerful ATi M18 and the chipset is the i865G if I can recall with Dual Cheannel 2x 512MB DDR 400 from Infineon.
Dual OpteronDP 248 CG Sledge Hammer's 2x 2205Mhz , 2x 1MB L2, 2x 3x16Bit 800Mhz HT Links & 200mhz FSB. These are used for my Long Live the AGP Bus project
it has a Sapphire ATi Radeon HD 3850 AGP 512MB GDRD3 & a 3dfx Voodoo5 5500 PCI Macintosh 64MB SDR for the retro games I do with it.
Dual OpteronDP 285 E6 Italy's. 4x 2616 Mhz, 4x 1MB L2, 2x 3x16 Bit 1000Mhz HT Links, 200Mhz FSB. This is my main system it's mainly built ofr Flight Simulator X Deluxe Eiditon it has a XFX-Pine Nvidia Geforce 9800 GX2 PCI-E 1024MB GDDR3 XXX Edition, This machine runs Vista Business 64 + SP1 UK and it runs FSX DE @ 1920 x 1200 x 32 + FSAA x4 & AF x16 in max settings without a hitch in DX9.0c though, this system will; get an upgrade with a Geforce GTX 295 & more ram, because I'd like to use the same settings for DX10 hehe.
The Mobo it uses is an ASUS K8N DL with 2x Dual Channel DDR 400, which is DUal DDR 400 per Dualcore CPU, it'does an effective 12.8 GB per sec memory bandwidth in FSX which easilly can keep up with a Phenom 9950 Black Edition heh I ran FSX on these both to find out and It was rather amazing that a server based system of 2006 could keep up with AMD's best of 2008 for the gaming market heh. the chipset the K8N DL has is the Nvidia NForce Professional 2200 aka NForce 4 Pro.
Both retro and new stuff here . Although my Opteron's start to age as they are over three years old now.
Currently I'm using an Intel Pentium III-S 1400MHz 'Tualatin' CPU (this one) for my 3dfx PC. The CPU is the 'server' edition (III-S instead of III) so it has 512KB L2 cache. I noticed the CPU is quite a good performer for 3dfx cards using the 3dfx reference drivers. Too bad the Voodoo Graphics and the Voodoo Rush doesn't seem to run in the system but that's not unusual. It's incredibly difficult to get a Rush board running in a 'modern' system.
Your dual Opteron 285's aren't so much different compared to my Opteron 2218 ES CPU's. They both run at 2600MHz and are dual-core. Although I have socket F (1207) with ECC Reg. DDR2-SDRAM running at 333MHz (DDR2-667 / PC2-5300). This al runs perfectly with an onboard ATi Rage XL and just the 'Standard VGA Graphics Driver' from Windows Server 2008 . I have no means of playing games on that system as it's not designed for it . For games I have my workstation/desktop PC.
well Simulators are not games as any Flight Simmer would say hehe FSimulators are based to simulate the real things and games are morely based on fiction
and really for Flight Sims I do advise such setups , as it runs FSX DE for 21 hours flatout no hickups nothing, I had lesser successful events with high end desktop setups so I totally stepped as far away from that segment as possible.
the Bios chip is socketed which is a very important feature even more reliable than dual soldered bios chips because if they both fry you're still in trouble with a socketed bios you remove it with a PLCC bios extractor tool and click in the new one and you are ready to go again, this is a major advantage with any workstation & server board, they all have this.
And they are famous because of their speed & stability in highly stressed applications as well, so yeah just for those things I prefer these.
oh btw all the parts for the Dual Pentium Pro are in transit
I have updated the Pentium Pro 133 topic for that part hehe since making a new topic for just that system wasn't really on my mind hehe.
Pentium Pro's will be a new experience for me hehe.
Based on the layout and specs of the ASUS K8N DL I'd say it's a tad more 'workstation' setup instead of 'server' setup. You have a LPT port, on-board audio and expansion slots (PCI, etc.) are more like a normal PC/workstation. My Tyan Thunder n3600R has only one usable PCIe slot and no onboard audio. It's more 'server' then 'workstation' thus games / simulators are better of on my desktop PC.
The dual Pentium Pro would be good for retro-flight sims .
hehe you bet though the K8N DL does have 2x Dual Channel DDR 400 support, 6x 4GB PC3200 ECC Reg max memory support 4x SATAI 150 + 4x SATA II 300 + 4x IDE UATA 133 & 2x FDD support and for a server this simply exceeds to those standards, the PCI-E x16 can also be used for an ultra high end SSD Raid controller PCI-E x8 card and for the VGA card a simple 16MB Matrox G450 PCI for example it is definitively a server board hehe .
there are even Quad Opteron MP mobo's with onboard sound & LAN these are normal things you'd come across almost on every mobo workstation or server based hehe.
bur for the Dual P Pro 200 1MB I have these flight sims
DiD F-22 Air Dominance Fighter
SSI Flanker 2.51
Micro-Prose Falcon 4.0 + Supa Pack 3 & Free Falcon 3.2