Speed is mostly depending on power vs. drag. Heavy aircraft were fast if the p/d ratio was good, talk P-51. Rate of climb is very dependant on weight vs. power installed, so we have the slower Spitfire IX out-climbing the heavy Merlin Mustang; American fighters tended to be heavier than European fighters.
XP-46 was reasonably fast for the power installed, but not fast enough to justify the switch from the in-production P-40 to the P-46. We don't know enough about the RoC, we also don't know enough about the aircraft condition during the tests (presence of protection, radios, guns, ammo, ballast?)
Yes, the non-turbo V-1710 was getting well behind the curve by second half of 1940.
XP-46 was reasonably fast for the power installed, but not fast enough to justify the switch from the in-production P-40 to the P-46. We don't know enough about the RoC, we also don't know enough about the aircraft condition during the tests (presence of protection, radios, guns, ammo, ballast?)
Yes, the non-turbo V-1710 was getting well behind the curve by second half of 1940.