I have Gohan with a small power advantage. If he was 100% serious and with the intention to kill Cell, he should be able to win after an extremely difficult fight.
Similar to Goku vs. Tien at the 22nd Tenkaichi Budokai; Gohan is the stronger fighter (though in his case, it's mainly due to being more powerful) but Cell has better technique.
Gohan wins in a h2h battle but it wouldn't be a easy. Maybe something like suppressed Cell vs MSSJ Goku... Towards the end an obvious difference would be noticed but Cell would put up a respectable fight.
While Gohan was in need of external motivation, I think Cell's attitude was a roadblock for him also; he was too high off that power. Goes either way IMO.