AMD Am386 SX40
A typical 386SX motherboard with a AMD Am386 SX40 fitted. The chip is dated 31 week 1994 so this this was used for a budget system of it's day. I guess the 40MHz clock favored the sales somewhat since a higher clock is often regarded as a faster system. Nevertheless, the 386SX in essence isn't really faster than a 286 (hypothetically at 40MHz).
I haven't benchmarked this motherboard yet but did run benchmarks on a different one with different chipset. See the benchmark link for the results.