A MTB crankset with Aksium wheels will give you a bad chainline. MTB cranksets expect a 135 rear wheel and put the chainline out accordingly.

The 520 brake levers are meant to work with linear pull brakes, and you should take advantage of that. Get some Avid Single Digit 7's. You'll like them much butter than the CR720s.

I personally think your gear sounds way too low for the type of riding that makes sense for a cyclocross bike. You either need a mountain bike or higher gearing, IMO.

Unless you've found a really good deal on the XT stuff, I'd just use the new M590 Deore components. You'll be surprised how well they work. Espcially in the front where you'll be using friction shifting (or a road FD) the extra expense of XT won't get you anything but bling.

I've got an older set of Aksiums and have been very happy with them. They're tough wheels. I don't know if the new ones are better or worse, so I'd check reviews on that. Mavic quality seems to fluctuate as they come out with new designs.

Consider a second set of wheels and tires so that you can use slicks on road.

Otherwise, it sounds like a great build.