NEC V 30
Most XT-based systems are equipped with a 8088 class CPU or clone. Several other systems do their maths with the NEC V20 (a drop-in compatible CPU with the 8088) and older, more expensive, systems use the first classic 8086 CPU. The latter can also be swapped with a NEC counterpart: the NEC V30. Because most XT's were build around the 8088 CPU, the 8086 and V30 are somewhat uncommon these days.
The difference between the 8088/V20 and 8086/V30 is the external databus. 8086/V30 has an 16-bit external database for faster memory access. The 8088/V20 is basically the same but with half the datapins (thus 8-bit).
The NEC V20 is a reliable, cool running CPU that runs somewhat faster than the original 8088. I always wondered what a NEC V30 would do: I benchmarked it and it runs great! Even at 8MHz it surpasses the 10MHz TurboXT V20! It seems that the 16-bit bus really makes a difference with the NEC V30 .