If Nash is all he's supposed to be, he should be able to more than make up for any deficiencies he'd have on defense with the edge he'd have on offense.
A legitimate NBA small forward with his size/athleticism should be able to punish the typical Big 12 power forward offensively. There does appear to be a decent amount of talent at the 4 in the Big 12 this season, but we're not talking about a ton of future NBA players. They're good college players. A guy like Nash should be able to handle that. If Kim English can make that work, Nash certainly should be able to. He has the size, athleticism and talent to do it.
(Ford coaching him to actually do what he's capable of... that's another topic; sometimes I forget who's coaching OSU)