After downloading the trial for FSDT JFK v2, I noticed something around the New York area was absolutely reeking havoc on my system. Such low FPS, like 9-12. I knew from the start it wasn't FSDT, because when I flew further into the City, it stayed the same.
Anyways, the culprit was ImagineSim's old Newark Scenery. I forgot I even had this installed, because I never really fly in this area. (Until now). Disabled the scenery, now FPS are back up into the 50-60 range!
So I encourage, if you are having strange, unusually low FPS in the area of New York when spanning over certain areas, check to see if you have ImagineSim Newark installed, because I've checked this on 2 different computers now, and the result is devastating on the frame rate. (Most likely because it's for FS9)
Also, I encourage to uninstall Aerosoft Manhattan, for the marginal eye candy that it has, the performance hit is not worth it.
Happy Flying!