Why should Spitfire fans have to use a fighter from mid-1942 against late 1944/early 1945 monsters?
Most of these unperked late-war "monsters" you speak of have top speed as their *only* real advantage against the XVI, and for many that is not even the case. For instance, the P-38L, 343mph on the deck, P-47D-40, 340mph on the deck, 190 A-8, 349mph on the deck. Speed margins either non-existent or too narrow to give any practical ability to disengage from a SpitXVI with closure on you. As compared to the other so-called LW "monsters", many, if not most Mid-War planes actually perform better in maneuvering...the exception here being the SpitXVI, whose ubiquity I argue kills the viability of planes with "mid-war"-ish combinations of decent speed and decent maneuverability. The SpitXVI and La7 are the "monsters of all monsters" amongst the unperked. The latter at least is somewhat self-regulated by fuel range and horrible ballistics.
As to your perk reference, Spitfire fans already have a perked Spitfire, the Mk XIV, and look at the stunning usage and success numbers for that thing.
The SpitXIV quite possibly deserves a lower perk price, what is your point? The XVI is arguably the better plane for the MA.
I propose the VIII remain unperked, because although its performance is superficially similar to the XVI's, there are lots of little points where it is inferior, especially roll-rate at high speed, which I think add up.
Oh, btw, before we go any further, I don't hate Spitfires, don't call people flying Spitfires nasty names (the tool is there free for anyone to use...), fly Spitfires in the MA myself, grew up reading about the Battle of Britain, *and* I have a copy of "Spitfire", 1942 with David Niven and Leslie Howard, which I have watched many times and could go into my video collection and put my hands on right now.