I am currently using Corsair AX850, it seem to have coil whine sometime under full load. Before this I did some research if 850w would be enough, the opinion vary. Some say it will be enough and some recommend at least 1000w just to be safe. I know since the PSU is over 1 year old, it have possibly deteriorate 10%.

I did some stress test, the rig seem to be running fine in Crysis 3 and Metro Last Light max setting. I ran some benchmark, Resident Evil 6 benchmark, Unigine Heaven and Valley. They work perfectly without driver crash but when I attempt to run 3dMark Fire Strike Extreme, it just totally crash after about 20 secs, black screen appear and I have to restart pc. I am not sure if it's an issue with sLi, the latest Nvidia beta driver or my card just can't just draw enough power to run the benchmark.

What do you guys think? I am afraid that even though the PSU is not giving any problem now, it might just fail all in sudden and maybe even damage my hardware.

Some of the PSU I have in consideration, budget around 1.1k.
Corsair AX1200i
Seasonic P-1000
Seasonic X-1250


Current rig
i7-3770k @ 4.2ghz (Keeping it there for now as I am afraid going further will push the PSU too far)
GIGABYTE Z77X-UP7 (2 x 8pin CPU power plugs, but only 1 is required to be used so I just plug one in)
GTX Titan sLi @ 1163MHz/1.21v (Default Titan pulls about 250w, I would assume with my overclock its pulling a maximum of 300w each)
D5 Vario pump @ maximum speed (Should be 37W max)
4 x 140MM Bitfenix Spectre Pro non LED & 2 x 120MM Bitfenix Spectre Pro non LED plugged in 30-watt fan controller on NZXT Phantom 630 (So I am guessing they would only draw 30w max?)