"NEC #V20 vs Intel 80186"
Also covers the #V30. #Psion moved the SIBO architecture from the 8086 in the MC range to the #V30H in the later models, such as the Series 3. (#MAME development of the SIBO emulator has shown that EPOC16 does use the extra V20/V30 instructions in later versions.)
With EPOC32, Psion moved to #ARMv4 in the Series 5.