Phoronix pits Fedora 15 against Ubuntu 11.04, you can check it out over here.
"Ending out May, we have an interesting set of tests comparing
the performance of Fedora 15 and Ubuntu 11.04. This is looking at the
"out of the box" performance of both operating systems on three
different systems. Not only is the actual test result looked at, but we
also compared the power consumption of the two operating systems."