Speaking as someone who's trained in Ringen (medieval German unarmed techniques), Langeschwert (medieval German two-handed sword techniques) and Highlands Broadsword (18th Century, one-handed sword, no off-hand weapon) - there's more overlap than you think. The key elements are an intuitive understanding of distance and timing, and training for that in one particular situation is still training for that. "Never give a sword to a man who can't dance," as the saying goes. (The internet attributes this to Confucius, though I'd always thought it was Voltaire.)
On the other hand, Sulu's sword skills are generally shown to be Olymic epee or rapier, and those sports tightly constrain what you're allowed to do, to a degree that it can actually hamper you in a no-rules fight.
On the griping hand, both Kirk and Sulu are honourable men who believe in the ideals of Star Fleet, so the actual answer is "neither," because both men have the skills to avoid accidentally killing an opponent and both men would stop fighting when their opponent was disabled. The entire point of Trek being that we can find solutions without violence, etc, etc.
As to who would disable their opponent? I honestly think both men are equally skilled; neither engages in close-combat as a routine task, but also neither is incompetent. They're also of similar height and build, and yes that matters - all else being equal, a good big man will beat a good small man every time. We have more examples of Kirk than Sulu, but very few examples of Kirk vs Sulu. And I don't think we can use the Mirror Universe examples, since that's clearly a situation where being better at hand-to-hand directly contributes to being promoted.
So who would win? It would depend on external factors: who was more rested that day? Who was less distracted? Did they both start fighting at the same time, or did one get a couple initial blows in before the other realised there was a fight at hand? Is one in easy-to-move-in casual wear when the other is in encumbering formal wear? And so on. Set all those factors to equal, and it's a coin flip.
