Those are great PSUs. I have the X750 and really like it. Mine is plagued with a high frequency coil whine, however I don't think that is entirely the fault of the PSU (likely a PSU/MB interaction). Regardless, I would still recommend it as long as you don't rely on the PSU fan for proper venting of your case. The fan on that PSU only runs at high loads, so it makes a great bottom mounted PSU. My other favorite is the old Corsir HX650, however it is only a bronze level (efficiency) PSU.