[vanir]

From what I've read the main benefit of the MkII was increased armour with no loss in performance due to the more powerful engine (ie. it evened out for the same performance as the MkI). I guess its importance in Il2 depends on how well the armour is modelled in comparison to the E-3 mod and E-4 in game. If the E-3 has lighter armour than the E-4 and the Spit MkI mod has been modelled correctly for armour roughly equivalent to the E-1/3 then a MkII is justified to bring equivalence to the E-4.

What I think is likely though (I haven't taken apart the files to have a look) is the MkI armouring was modelled more in line with the stock E-4 and MkV, so in effect the MkI mod is really a MkII anyway.
Hang on I'll have a quick look...

ladidadida...

Nope the MkI mod has the same armour as the MkV. It's a MkII.