Well it looks like the Corsair fans didn't fair all that well. The Noise Blocker is an optoin for sure but I would need a higher RPM version to make sure the video card stays cool. Under Load I don't know if 850 rpm will cover it.
Well for me anything over 800rpm stats to get noticeble, maybe not loud but for me there is no point going over that, i try to plan so i can balance on those fans, that said SPCR in that review also tested the S2, which is a 1200 version and also did well. Also they tested the GT AP14 1400rpm, there is a version 1150rpm that could be a solid option for you.
I imagine I can just throttle down the faster version with the Asus Fan control and build a custom fan curve?
Yes all of them can be undervolted with FanXpert fine,
M12 S1 and S2