Bicycle Mechanics - Maximum Capacity... Long cage, Med. cage?

I currently have my S-works CX cyclocross set up with a single front 42 and a rear 12-27 cassette with an ultegra med cage (broken due to locked pulley). I would like to get some more range because I want to keep it single up front, so I want to switch to an XT 11-34 and a single 44 front. My question is should I go with a long cage XTR M952 ($95) or with a long cage XT M750 ($57) or a med cage XT M760 (newest xt model) ($70). These are the options I can currently find to suit my needs in terms of price/performance. I don't know if the shifting advantage of a med cage outweighs the range advantage of a long cage. Is long cage for cyclocross just a bad idea? How do you calculate maximum capacity required? And finally, is XTR really worth the xtra money?

I have an XT long cage M750 with an 11-32 cassette on my Bianchi Axis and it works the way it's suppose to. The longer cage is necessary to take up the chain slack when going from 11 teeth to 32/34. I don't think a medium cage will handle the total chain slack between 11 and 34.

I was just looking at the shimano site, isn't the M760 low normal, i.e. Rapid Rise? That may be kinda screwy used in conjunction with STI style levers on a CX bike, or you may be using bar-end shifters.

I was just looking at the shimano site, isn't the M760 low normal, i.e. Rapid Rise? That may be kinda screwy used in conjunction with STI style levers on a CX bike, or you may be using bar-end shifters.

Yeah, it is rapid rise. I think that would be a little weird with STI shifters. A lot of people in the MTB forum claim that the XT works just as well as the XTR, it is a bit beefier (a bit stronger), and cheaper. The only dowside is a bit of extra weight.

I currently have my S-works CX cyclocross set up with a single front 42 and a rear 12-27 cassette with an ultegra med cage (broken due to locked pulley). I would like to get some more range because I want to keep it single up front, so I want to switch to an XT 11-34 and a single 44 front. My question is should I go with a long cage XTR M952 ($95) or with a long cage XT M750 ($57) or a med cage XT M760 (newest xt model) ($70). These are the options I can currently find to suit my needs in terms of price/performance. I don't know if the shifting advantage of a med cage outweighs the range advantage of a long cage. Is long cage for cyclocross just a bad idea? How do you calculate maximum capacity required? And finally, is XTR really worth the xtra money?
Go with the M750 XT It'll work just fine with the 11-34 cassette. As far as XTR goes I won't use it the durability isn't what is is with the XT components even if it is bit lighter. 207 grams for the XTR M952 vs 245 g for the XT M750

Medium cage GS derailleur has 33 teeth of chain wrap capacity. 34 minus 11 equals 23 teeth. You don't have to worry about the crank because you only have 1 chainring. 33 is more than 23 so you'll be fine with the GS.