Is Corsair TX750 enugh?

Probably. There aren't many things a corsair 750W can't handle. I think your safe. SLI can be taxing though.

Well it runs fine when not under load. But when i play BF3 and MSI Afterburner starts to rev up VGU fans i get all sorts og hangups

Do you have anything overclocked? If so try restoring your GPU/CPU to stock clocks, an unstable overclock might be causing your system to hang.

Have you tried running stress tests to check for stability (Prime95/Furmark at the same time)? Have you checked your system event log to see if you're getting any errors?

What are the temps (in furmark of course), how close are the cards.

all stock speeds. I did run stress test it was fine. It crashes only when fans start to rev up

Alright, run the test for atleast 15-20 minutes, see how hot it gets tell me if the fans ramp up.

if it doesn't try with a different stress testing software like OCCT or something. For that matter what were your temps and what program did you stress test with?