Using HandBrake we converted a 560MB mkv file to the mp4 format and measured the frame rate each configuration was able to achieve. The Asrock P55 Extreme4 and Asus P7P55D Deluxe both produced 59fps, which is an impressive result given that the Core i7 920 configuration was just a bit faster delivering 65fps.
The x264 HD Benchmark 3.0 is used to measure the performance of a 2-pass 1280x720 encoding, again displaying the results in a frame per second format. The results are all quite close in this test although P55 boards still came last. The Asrock P55 Extreme4 was found to be 2fps slower than the Asus P7P55D Deluxe in this test.
Using TMPGEnc 4.0 Xpress we converted a 715MB avi file to the mpg format and measured the time it took for each configuration to complete this task. The Asrock P55 Extreme4 was again slightly slower than the Asus P7P55D Deluxe, though the margins were quite minimal -- 9.23 versus 9.03 seconds on the latter.