I've had one of the stock fans fail.
Yes I had read they could cope with more then the 750 so they are within operating limits with the 4 ants.
I'm drawing 1680 Watts at the wall according to my monitor.

As they don't keep the ants cool enough even running at 190-200 gh they are only at about 34 with the new fans, I run two fans in case one cuts out, thus the ants don't cook them selves.
Also i'm not to sure how reliable they are, I've chosen a fan that I know is regularly used on servers and has a good reliability track record.