Widewing,
That was always my understanding as well. I'd always heard the spoilers on the 61B gave it a very high roll-rate, and that as you said, it could outturn pretty much in the US inventory. I threw those "borrowed" comments out for discussion because they seemed contrary to every bit of data I'd ever seen. Do you have any data comparing the P-61B to the C?
I have some information I dug up from the internets that suggests the following:
P-61A-10-NO onward (inclusive of the B-series) seems to have R-2800-65 Double Wasps with water injection. Max Power 2250hp each
P-61C used turbocharged R-2800-73's. Max power 2800hp each.
Unfortunately, the war ended before any C-models made it to combat. The latest version to see combat was the P-61B-20-NO (Targetting system upgrade), but I can only find two SerNo's assigned to that type. The most numerous seems to be a mix of B-10 and B-15 blocks, with the difference between them being the B-15's reintroducing the dorsal barbette.