Geist, you can actually get the info for most of the planes right here on HTC's webpage
. Go to Help->Game Overview->Planes, Vehicles, Boats (upper right).
This will give you a good idea of what various planes are capable of (speed and climb rate wise anyway) at various altitudes. Some folks have been doing research on turn rate and radius, and dive time, acceleration, and other stuff like that, but I can't remember the URL off the top of my head.