I oc'ed my nine B1 s7's since day one, out of the nine B1's four can hold 675 with low error rates. The others I had to move them in increments until they would be stable, then when one would drop after a few days I would drop it a bit. With the temps rising I have had to adjust them occasionally, but I have been getting 46.5-48.3 from them since early October with no failures.
YMMV, so it's a simple matter of balancing temp/hw error rates and fiddling with them until they are balanced enough for your own tastes.
Ufo