SOB,
At this point I don't think there ia a viable, non-perk British fighter. Even the 1943 Spitfire LF.MkIX would almost certainly be perked.
If the game focused on the most balanced year, when the war was still in contention, there would be lots of interesting aircraft from all nations that could be added. That year is 1943.
As it is, things like the Mosquito, Me410, Pe-2, ect, ect are simply going to be sitting duck targets to all of this 1944/45 stuff that the Germans and Americans keep getting (OK, all of the Japanese stuff is 1944 as well).
We already have example in the forms of the Il-2 and TBM-3.