The K4 (currently what we call G10) has speed and high alt performance going for it...
I personally don't find it that fast, and have rarely outrun much in it. The high alt performance is nice for when you're high enough to take advantage of it, but at those alts all RAF/USAAF planes turn better than it regardless of how the engine runs.
With only 30mm you may be right, wetrat, but don't forget it can also carry 20mm gondolas (one each wing) as well.
And then there's the climb rate, and the zoom capabilities. The K4 climbs extremely well (one of the best in the game with WEP) and can loop/zoom with the best.
So it wouldn't be immediately overwhelming, but as a total package I can see why some might want it perked.
I worry more about our current G10 than I do about the current spitV, because it's much faster and can climb much better.