ORIGINAL: adams
MDE 86 is correct.
They are essentially the same shaft. The pro series shafts are graded for .001and w/i +/- 1g, where as the xt are graded at .003 and w/i +/- 2g. Basically you pay a premium for consistancy. IMO the less variables there are, the more consistant your shooting will be. For what I spend on archery, spending $100.00 (on IMO the best shafts on the market) is money well spent.
Just my $0.02 on the GT pro shafts.
Adams beat me to it, that was pretty much word for word what I was going to say.
On another note, I've been using the Expedition Hunters for about the last year or so and have been pretty happy with them. They're only graded at .006 and +/- 2g. I've had a lot of success with them and for the price, I couldn't pass them up.