Verm, I'll do some acceleration comparison tests at lo alt.
About the other two points, substained climb rate is, IMO, a secondary factor in combat, as well as top speed. Zoom climb, dive and acceleration are much more important. Not sure about acceleration at lo level, but F4U4 is better zoomer and diver for sure at any alt.
I insist about the spits, SpitV is better than IX. Same zoom climb, same amazing diving, same or almost same acceleration, but SpitV is much better turner.