There have been a number of different xt hubs over the past few years. The 775 were ok for me but I've heard of some freehub failures. I think this model was also the first of their hubs to get an increase the number of points of engagement to 36. The newer ones still have 36 POE while the slx have 30. The newer hubs with 12mm axles have also had some issues with free hubs cracking in half... the recent trend of 36t+ cassettes is the major culprit.
However, the major question is will you be having these wheels hand built/custom built or will they be OE wheels? If OE and relatively cheap, say under $225, they are fairly decent wheelset for the price.
If you are having wheels built, I cannot imagine them costing much cheaper than $375-400. If this is the case you are much better off buying Hope Hoops from Merlin cycles or another uk online shop. Or, spend the money on quality hubs. It's not a place to skimp as good hubs can be relaced over and over.
Simply put, using shimano or SRAM hubs for a wheel build that will cost more than a few hundred is pointless. The main reason, they are not convertible to any other axle size than what they started out as, they are heavy-ish and they are not worth rebuilding on a new rim. I will never buy a non convertible hub again.