After setting to +1 I got about 1TH more for my 4 741's. Also hardware error is almost 1% lower for every device. I'm a bit worried of over-pushing my PSU's, because I'm using 1 piece 2400w Delta for every 2 miners. But so far no problems.
Happy mining BTC
Yeah, I think that's too much for the PSU.
I use two of those PSUs for three 741s.
M