I'd take Khan. Provo would have him in trouble at some point, but Provo was one of the worst finishers in history. He'd let Khan off the hook.
While the hate on Khan can be a bit much these days, realistically Khan would most likely punish Prov, and possibly get a stoppage on cuts.. He may get rattled or knocked down in the process though.. Khan got hurt by guys who caught him in between with counters moreso than people who were thudding type punchers (see the Maidana fight.). Provo has a shot as fighter like him ALWAYS have a shot, but safe money is on Khan.