I had a strong suspicion that it was the carrier that was causing the problem, as soon as it moves out of the shot the frame rate shoots up. I have a similar problem when flying Thuds over Hanoi. Fortunately I still have XP on my old PC, where leaving the carrier deck runs at around 20-24 FPS on an old GTX 295.
The low FPS kills this sim on Win 7, for me. I'll try a few more tweaks, but if there is no improvement in frame rates it will be an XP only sim for me.