G-10 dominates the Spit V (or IX for that matter) but others, especially its historical counterpart the 109F, have a tough time.
In the arenas (I dont do duels much, though I should do a lot more of them) I dont have a lot of problems with the Niki, I find the Ki84 a much more dangerous opponent to the Blue planes. The key to killing the Niki in an F6F (from my experience anyway) is getting slow faster than the Niki can get slow. Most folks never come out of WEP when they fight, so my best results come from chopping throttle, blowing E fast, and killing the Niki before it can slow down to my speed. The F6F is so docile and stable at slow speeds, even though it doesnt turn as well as the Niki at those speeds, will allow you to get a killing shot. This is how I fly many planes really, but especially the US planes with their excellent flaps, the P-47's, F4U's and F6F seem to work well flown like this as few expect it. If you run into someone good who sees what you are doing, its usually going to end up bad because they will go verticle and exploit your intentional loss of E.
In a duel environment, where the Niki can focus completely on you, this may or may not work depending on the skill of the Niki pilot. In the arena, if you dont kill the Niki on that first try, you MAY get another, in a duel you wont. If the Niki pilot is good, I'm with Redd, it dominates the Blue planes, as does the Ki84.
