I have XT hubs that have worn out two touring bikes. After five years I decided to clean and re-grease the hubs. When I looked inside, everything, including the factory grease looked so new I just put the hub back together and rode another five years, rain or shine. I am still riding on those wheels but the rims braking surfaces are well canoed and will certainly fail soon. I already have a new set of wheels with new XT hubs ready to go.

So I guess if you can get XTR cheap somewhere, why not. But XT hubs will serve you well. If I had to spend a ton extra for XTR I might take a pass. It is my understanding that the "R" in XTR stands for "R&D". XT is top of the line, XTR is the next generation "beta" version of the component. I ride an XTR long cage rear derailleur. It looks really cool, and I picked it up cheap. I would have been just as happy with an XT no doubt.