I haven't noticed any performance problems so far, on Lion at least. Are there some sites where it's particularly bad for you or is it slow in general? Is it just about loading websites or does even the app itself lag?
By the way, I just compared Safari 6 with Chrome 20 using
Peacekeeper and
SunSpider:
Chrome got about 3700 points in Peacekeeper, Safari only 2900. Though this big difference is probably because Safari doesn't support two of the video codecs. In general, the FPS were higher on Chrome, but in one or two of the tests Safari was better.
In SunSpider, they were nearly equal (158 (Chrome) vs 154 (Safari)), but for some reason Safari took way longer.