The P-38 fails to lead the pack in any single performance category, even in mid-war. It is a Swiss army knife and there are simply many skilled pilots who can seamlessly switch between the corkscrew and the nail-file when needed...
I did a few quick chart comparisons. It turns out the only plane that potentially needs perking in MW is the La-5FN, being as about as fast or faster than the nearest unperked British, American, and German birds in speed (Mosquito, P-51B, 109G2) at the typical low-levels and having a smaller turn radius than all of these rivals to boot. More lethality than everything except the Mossie as well. The La-5fn badly out-does the P-38J in every category until nose-bleed alts.
So if one is looking for an MW uber-plane to pick on, it is not the 38J. Heck, you should perk the 109G2 before you perk the P-38J.