I'd love to play a KOTOR which could last over eighty hours, but it might be too much for the main plot. Ideally I'd go with around fifty hours, but with enough optional sub-plots and side missions to make it last eighty if you wanted it to.
KNIGHTS OF THE OLD REPUBLIC : THE JEDI MASTERS
PLAY THE TOTAL CONVERSION MOD NOW! . | If you're interested, my almighty fanfic can be read here.