I'm positive that Fedor will win the fight, simply because of higher skill level. There are 2 scenarios for the fight.
1. Choi never really took any big punches. He has huge reach and simply to tall for his oponents. Fedor will dictate the fight from the very beginning and will land few body kicks/punches and then a big hook to knock the big man down and finish up with some G&P.
2. At some point in the fight, most likely first couple of minutes Fedor will try to take Choi down (this is where his Sambo experience will be a huge factor) and once he does it's a matter of time before ge goes for an arm bar or a choke. (Most likely scenario)
However, there is a chance that Choi will simply catch Fedor with a punch and finish him up with knees. Unlikely though.
that is the only way, knees