I don't have recent Iphone4 GPS airborne test results but I can tell you that the Ipad2 GPS is truly crap.
Today I flew along the south of England and after it initially got a fix (within a minute or two) it later lost it, in a subtle and non-obvious manner.
I have never seen a GPS do that before. This is really useless.
I have a bluetooth GPS which is connected to a proper rooftop antenna, but the Ipad2 does not recognise it at all - not even as a bluetooth device.