Aubrey,
If you are going fast enough to be in the tunnel, then you have no turn advantage vs a 51 who is at the same speed. You have to remember that all planes are limited by the 6G blackout. If you and your opponent are both going 275 MPH, and both pulling 6G's, you're both turning the same size and rate of circle. Neither plane has a turn advantage at 6G's.
It's when you get slower where your FM-2 can pull a max of 3 Gs that you have the advantage, because if the most your FM-2 can pull is 3G's, then the 51 probably can't pull more than 2.25 or 2.5G's. You will out turn him.
The quick answer is, you both have to get slower than about 225 MPH for the FM-2 to have a turn advantage.