subtle difference?

Could someone tell me the main difference besides $$$ between Celestron's 80mm. C80 ED and the Celestron 80mm. ONYX
thank you, John Meiners

C-80 ED is a f/7.5, 600mm fl with a R&P focuser, Onyx is f/6.25, 500mm fl with a crayford focuser. The C-80ED is believed to have a fpl-53 element. The Onyx has Fluorite based, low dispersion glass. Guessing it's fpl-51.

I think it's safe to say the C-80 ED will have better color correction.