A format seems to have solved all the issues, did a format a couple of hours ago and I'm still installing all the updates. Ran stone giant perfectly fine this time and the Physx tests all work well, it seems to have been a driver issue. Once all the updates and service pack is done, I will post some scores, although at first glance stone giant seems to have gone from a 55 average to a 102 average so thats quite some gains there
Dayum, They have an SLI pack for 170ish GBP on today only, Seriously considering this as it will probably be cheaper than shipping my 660 off to EVGA in munich
That's a fricking INSANE price for those cards, thats £240 for what is effectively equal to a 780GTX (sli 580's) (except the vRam, I keep forgetting I have 3GB cards)
Dude with one 580 I play bf3 at everything maxed out and I get a minimum of 40fps at 1080p, so I'm pretty sure you'll be fine, maybe you'll have to kick AA down a notch but you will NOT be playing it on minimum.
On a side note, here are some unigine benchmarks I just did at stock.