I believe the 800 has a magnetic weather seal and slightly better air infiltration numbers than the 500. It's a little nicer looking with lift handles rather than a lift rail. Otherwise they're pretty close.
Nothing wrong with the Gorell 5300 either.
Right on.. You trade .01 in U value, but gain better structural #'s due to the magnetic weatherstripping and sash reinforcement. That, plus it is definitely more attractive. Go with the deluxe package either way...
I'd also agree that you can't go wrong with the Gorell either.