Just to elaborate on Darryl`s Mosquito story :
We have a guy who wins almost all our races, whether he sails uni or sloop. He can make the boat go fast in both configurations, such that the rest of us can`t beat him too easily, either way.
Now, I can sail sloop faster than I can sail uni, so it`s different for me, but that could be a factor of my weight since I`m quite light, and struggle a bit uni in over 14knots.
Another thing: in over 12knots uni can outpoint sloop, but sloop goes faster, so VMG to the A-mark is about the same, and downwind they are so similar up until about 18knots, where uni struggles a bit to keep the bows out, less weight on the rear beam perhaps.
Good sailors still get to the front. Worrying about whether all the boats are exactly the same usually puts you somewhere in the middle of the fleet, because you`re too busy looking for excuses not to do well.