One thing I still do is disable the NY add-on airports I'm not using for a particular flight

To add to this, remember that in the NY area you have 3 major airports and if you have addons for all three that is already very taxing and considering their close proximity FS9 may have all 3 loaded fully at once. In addition there is traffic coming from all three and ATC has to attempt to keep all these flowing (AISmooth may help here). Finally there is the city's scenery which if you're using the FS9 Aerosoft Manhattan or another addon puts in a fourth scenery area the game must have loaded since NY is very visible from LGA and JFK probably EWR too but I never fly there. Then comes the last big bang to your system and that is your complex airliners with highly detailed virtual cockpits and complex systems that are very CPU intensive. Now a system like yours should be able to handle all this pretty well and at LGA 19fps does sound low but not to an extreme.

Did you install your chipset drivers?