In identicle situations, a kill in a P-40C is going to be more impressive than a kill in a Spit XVI. I don't care if we're talking about a rather high-speed fight where the spit is starting to get some heaviness on the controlls; its still a P-40C, with about the same firepower as one of the spitfire's cannons, and no reall preformance to speak of.
So, had those 10 kills been made in the same manner, but in a P-40, or a C.202, it would be even more impressive. Basically, how the kills were made is entirely irrelevent to the discussion, as we're just talking about a different plane making them in the same situations, not changing the situation.