While a lot of exciting changes have been introduced, for the test system I used for this initial benchmarking (an Intel Core i7 4770K "Haswell" with AMD Radeon graphics), the results weren't too interesting thus resulting just in this brief one-page article. In this initial benchmarking on the same hardware I compared the Linux performance of the 3.12, 3.13, 3.14, and 3.15-rc1 kernels for representing the latest-generation Intel CPU paired with a Radeon R9 270X graphics card on its open-source driver.
The results, as you can see by checking out the OpenBenchmarking.org result file, aren't too interesting. There's little change out of the run-time performance in the selected benchmarks when comparing the past few kernel releases. Beyond that, leading to the on page article as well, was the fact that the Radeon graphics testing failed. As shown below, there was some corruption when running with this R9 270X card while with a Radeon HD 6870 the experience was ultimately producing a lot of noise on the screen.
Those wishing to checkout the early Intel Core i7 4770K results from the Linux kernels from 3.15-rc1 going back to 3.12 stable can see them via 1404159-KH-LINUX315K27. Overall, there isn't much change but more benchmarks will come once the Radeon DRM issues get sorted out and there's been more time to test the Linux 3.15 development code on other platforms.