The hardware differences between the GA-H55-UD2H and GA-P55M-UD2 are minimal. After running both boards through our rigorous testing procedures, we can see that the performance differences are also fairly minimal, however, the P55-UD2 was clearly happier in its overclocked state than the H55-UD2H, making it still the budget Lynnfield overclocker of choice (both are mATX boards). The only real reason that you'd want to opt for the H55-UD2H over the P55-UD2 is that it brings Core i3's integrated graphics chip to life, as it features a broad selection of video out ports on the rear I/O.
The loss of RAID-capability and a few SATA ports won't cause too much of a stir for most people, but if you wanted to back up your media collection for a media PC then you'd need to make use of that PCI-Express x4 slot for a RAID card. Neither board produced spectacular numbers in the gaming results, though they at least managed a playable frame rate in Crysis at 1,680 x 1,024 with 2x AA of 25fps. However, the Asus P7P55-M was a good notch faster than these boards, though it will set you back an extra £10 and we found it doesn't generally overclock quite as far. Moreover, the Asus didn't perform as well in the 2D benchmarks, lingering towards the bottom of the graphs in all tests.