For me, 1600 Mhz is fine. Not noticible in daily use with higher, that I can tell.
what I would do, if I was you...
Set turbo to "per core", and up the multi one at a time using the same multi for all core manually set in teh boxes that appear, boot into os and run LinX or IBT with max memory selected, to find out where it begins to throttle. I sugget about 10 laps of LinX with maximum, and then watch to see it drop.
This will let you know what speed you can hit before the power consumption limits are hit. I'd use that as my OC.