Phoronix has finished doing a massive Linux Kernel benchmarking. It tried to benchmark since Linux Kernel 2.6.12, which is five years old and up to unreleased version of Linux Kernel 2.6.37 which has just entered stabilization phase after Linus released rc1 which also ends the merge window phase. In total, they tested around 26 Linux Kernel using several distros. Check the report on Phoronix.
I kinda dissapointed with the results, since in the last few release, there has been a major regression which reduced the Linux Kernel performance according to the benchmarking. I hope with further release, the performance will come back to normal again. People is not always for new features, but also increased performance as well