This was quite interesting. I was modding the BIOS on my new Gigabyte P35 DS3P and had installed a Xeon E5440 with the un-modded BIOS. It seemed to perform pretty good and so I made some Minecraft 1.6 framerate benchmarks to test the before-and-after BIOS mod CPU performance. Got the R9 270X installed so there was no issues with GPU limitations.
Standard F12 BIOS:
TEST 1 - 87.6 avg, 46 min, 140 max
TEST 2 - 75.5 avg, 49 min, 92 max
Modded Xeon F12 BIOS:
TEST 1 - 112.6 avg, 53 min, 176 max
TEST 2 - 93.5 avg, 79 min, 121 max
Never expected to see that kind of performance boost. A lot of those numbers went up 30fps (including minimum FPS for Test 2 which was crazy) and it's like a totally different machine now. Also tested Cinebench R15 but it remained identical at 300cb, but not surprising behavior from a synthetic benchmark.
Minecraft isn't the ideal benchmark tool, but it's the only decent CPU-intensive game I've got and it's great for testing LGA775 systems.