Only argument I'd make for perking is the 3-cannon option, which was used in all of 300 or fewer La-7s.
I disagree that the Spixteen is one of the best fighters in the game. The top speed as you pointed out is generally is mediocre, and while rate of roll is spectacular the Spit IX and V are superior low-speed turners (some argue the VIII is as well, but I find the VIII one of the easier Spits to deal with, fourth after the Mk.I, Seafire, and XIV in that order). Her main advantage, like most of the Spits, is that she's easy to jump into. But there's enough aircraft that take more work to learn that are much superior once you learn them (Ki-84 comes to mind. I hate running across a VERY well-flown Frank more than almost any other aircraft).