I don't believe there's any fundamental differences between the '04 and '05 models. All things being equal, I'd personally lean toward the later model year with fewer miles, but you gotta go with the one you like... As with all BMW's, mileage isn't as important as the maintenance history; if the one with the higher mileage has a more comprehensive maintenance history, that should influence your decision accordingly. And incidentally, I suspect that the vehicle listed as "black" is actually Carbon Black, which is a actually a very, very dark blue; if you want a conventional black color on your M3, you might need to search a little more.
Before purchasing either vehicle, you'll want to research the forum for some of the potentially expensive problems, like VANOS failures (screws backing out) and subframe cracks. A pre-purchase inspection by a qualified independent BMW mechanic or BMW dealer is highly advisable.
X3 w/6-speed & Sport Package:
A sports sedan disguised as an SUV...