So I need a new rear hub and I don't want the same one, but I also don't want to have to buy new spokes. I am planning on just rebuilding the wheel with a new hub (have the tools).

It seems the XT FH-M756 rear hub is the exact same dimensions as the Deore M525 rear hub so the spokes should work. I would just like to double check to make sure I am not missing anything before I order it. Here are the hub specs.

looks good.
Shimano doesn't really change specs too much between their hub series, until you get to the highest end, which is XTR/DA or there is a different type of brake used.

https://www.mrrabbit.net/wheelsbyflemingapplications.php

Grab the Spoke Chart spreadsheet....

=8-)

It looks like you are wanting a Shimano freehub that takes a six bolt brake rotor. You have few choices. You could get another M525 or the M756. There are very few differences between those two. Of special note, the Body Fixing Bolt is the same in both.

You might want to check the M529 hub. That's the "stronger" "29er specific" six bolt rotor compatible hub. It isn't clear what's stronger in the 29er hubs. One might presume that the freehub bodies are different, but no, Shimano uses the same part in 29er and non-29er hubs. I suspect that the difference is in the actual hub shell.

Do you think the 20$ price difference is worth it between the 2? My M525 failed but there is no way to know if this was caused by the wheel's former owner (the hub bolt was not attached to the hub), or if the XT hub would even have made a difference if in fact the bolt stripped itself.

525 vs 756 is some machining differences(speed holes,cone finish etc) and an extra seal. the 529 freehub body is 32 points of engagement vs the normal 18 or whatever it is.

Better freehub on the 756, better sealing, better axle too, I'd spend the extra money (and I did).

Is that the difference? I'm wondering because the info I have on the M529 and M629 hubs is that they are designed to withstand the extra torque the new 12 x 36 mtb cassettes generate, but I don't have any info on exactly what the difference in their design is. These new cassettes with the extra large cogs are fairly common on 29er mountain bikes because of the difference in gear inches the larger diameter wheels make.

So they've designed these hubs with extra points of engagement and that will presumably help with the extra torque loads?

DO NOT GET ANOTHER 525 NO MATTER WHAT. I've never seen more bad reviews for something than i've seen for that rear hub. they are absolutely terrible. the 29er specific hub as menitoned above was designed to handle the torque stress that a 36 tooth casette cog can put on. if your running that big of a cog, you may want it, otherwise you probably don't need it.

Thanks, never shall I ride an M525 again. I will throw its guts to the curb and ride over em once I get my 756