Well, Coldfeet -
I put my Nashbar CX frame/fork in the workstand and measured as best I could with a steel rule...
At the "shoulder" where the fork legs begin to curve there is 50-52mm of clearance.
From the top of the dropouts to the inside apex of the crown measures 365mm of clearance.
I am currently running 700x35 Panaracer Pasela TG's (a touring tire) mounted to 36-spoke Mavic A719's with XT hubs on that bike. That combo leaves at least 5mm clearance to either fork leg and about 16mm clearance to the crown.
I have had some 700x40 knobbies on there with no problems (I'm running BB7 road disks). I think you could run 700x44's based on that...
The Nashbar fork is built very stout - and weighs accordingly. I use the bike as a year-round commuter and long-distance event machine. I don't race CX, so I can't comment on that application. All-in-all, I'm very happy with the fork - and the rest of the bike as well.
Hope this helps.