I just bought the Crosshair III from newegg.I got it over the M4 because it appeared to be better laid out (based on the M4 review, most of the complaints about the layout such as sata orientation appears to be corrected in the Crosshair III). My second reason was because I plan on OCing my other components at some point and it appeared the CIII was the best choice for ease and intuitiveness.
I got the Phenom II 955 BE and 8 gigs of DDR3 1333 as well as 2 ATI 4850 1 GB cards so well see how the build goes.
Just as side note that may affect your decision-DDR3 1333 appears to be the crosshair III's preferred speed and it(online manual) stated 1600 can be reached by overclocking. I donít know if itís designed to accept native 1600 Ram without OC (easy enough if you already are using ram designed for the higher speed, but still). Might be something to look into because I donít know for sure to be honest. I donít know which speed of ram you were planning on getting so I thought id mention it.