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First of all: despite being socket 7 (PGA296) this CPU is not compatible with normal socket 7 boards. If you try to use it in such boards you may end up with a fried CPU!

The Cyrix MediaGX is based on the Cyrix Cx5x86 CPU core with hardware to process video and audio output (XpressRAM, XpressGRAPHICS and XpressAUDIO). It was used in some laptops and Compaq Presario systems.

Eventually the technology ended up at AMD's since AMD bought the technology from National Semiconductor in 2003. Both the Geode GX and Geode LX are based on the MediaGX core. The Geode NX is different and based on AMD's own 'Thoroughbred' core that was used for the Athlon XP.
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Technically the same as the IBM 5x86C.

Because the Cyrix 5x86 uses a scaled down version of the M1 (6x86) and thus having some Pentium instructions this CPU is able to run the benchmark of Murder Death Kill (MDK). Note that the benchmark states it requires a Pentium processor. This makes the 5x86, along with the Pentium Overdrive (PODP5V83), the only socket 3-compatible processors that can run MDK. > Read more

The IBM 5x86 is technically a Cyrix 5x86 processor. The 5x86 is based on a scaled-down version of the M1 core used in the Cyrix 6x86. It provides 80% of the performance for a 50% decrease in transistors over the 6x86 design. It's some sort of 586 on a 486 socket as it uses the 32-bit memory bus of a 486 (Pentium had 64-bit) but internally it even had some (limited) support for Pentium instructions. Some features of the 5x86 that could improve performance are disabled because they could be potential bugs which were not fixed before the release of the CPU. These features can be re-enabled using some utilities.

The 5x86 doesn't run in every 486 motherboard. Besides support for the lower voltage the BIOS also needs to know how to handle the 5x86 CPU. > Read more