I know everyone thinks the new XT's are the be all, end all brakes but its not all about brute power. I have had the current XT's and loved them once I got used to them, but they are basically an on/off switch with hardly any modulation.
The new 4 piston Sram trail brakes have comparable levels of power but due to the dramatic nature of the XT's they feel much more powerful.
If you do not have experience trimming the lines and/or bleeding them, do yourself a favor and take them to a shop after install to get them set-up right. Then enjoy.
Lighter than the XT's and the new HS1 rotors are light and quiet on my bike. I went from 180mm fr/rr XT icetech rotors to 160mm fr/rr HS1's with the X0 trails, that says allot.
I'm a big rider, about 230#, and they work perfectly with no fade anywhere I've ridden, even with the smaller rotors. And they have gotten rid of the CPS washer system on these, nice.