Keep testing Jekyll, you'll get it right sooner or later.

You dropped about 350 feet during the 360. Which over a 16.7 second turn is about the same as having an extra 300 hp accelerating the plane!
Doing
level turns starting at 300 mph, 50 feet altitude, WEP on, I get 275-285 mph after a 180 in the N1K2-J and 265-275 mph after a 180 in the Fw 190A-5.
Search for Wells' "Energy Retention" thread if you want to see how to do this kind of testing properly. He's got a really good method worked out which is better than doing 180's on the deck.
Also Wells did some calcs to show which planes should do better than others in this kind of thing. Not surprisingly, N1K2-J and Spitfires were on top. I've yet to see a comparison of planes in AH (with each other or with real life experimental data) that didn't make sense in light of Wells' calculations.
<S> Glad to see someone looking at this scientifically instead of with whine-ology.

[This message has been edited by funked (edited 11-28-2000).]