Seriously, if you are looking at overall performance, looking at Portsmouth, or PHRF ratings, gives you a ballpark of "comparative performance," or performance compared to other boats in a given W/L type course... It's not perfect, but it'll give you a ballpark.
The fastest boat on the water 'should' be the new (seriously new, she just got Her mast today) 100' Comanche. She was built to do nothing but wil line honors is ocean races... Of course she is also probably $10 million to build plus $1 million per year to operate. Maybe more.
The fastsest us mortals can probably afford would probably be the GC32 foiling catamaran. Which is a much more reasonable $250,000. Even cheaper but still rocket ship fast would be the Flying Phanton another foiling catamaran but more like $40,000.
After that there are a lot of fast boats that aren't quite so technical and can be sailed by meer mortals. Melgus 24, VX OD, Martin 243, ect...
Where you sail and in what conditions you sail in will have a lot to do with buying the right boat for the conditions you are in. A great heavy air boat may not be so great if you constantly have light air conditions.