Ended up getting the black Fire Mountain. Besides having a rebound adjustment, the XCR also has slightly beefier stanchions (32mm vs 30mm). It doesn't sound like much, but they are noticeably bigger just by looking. So all things in consideration, I opted for the better fork hoping that this way I won't need to worry about upgrading it. The Altus drive train shifts just fine, and it's easy enough to upgrade a derailleur if need be.

Thanks again for the input -- it definitely helped in the decision-making.