Yes, did that very test last night. In 1920x1080 flat screen, in Fenix at LGA I was getting around 35 to 40fps on ground with NO VATSIM, and no FSTL, and slightly higher in the air.
When I turned on FSTL and Vatsim (LGA was vey busy on VATSIM), I was getting 30fps or so. While taxying. Never below 28 fps or so.