Cool, that's a good OC. 7850 IS a good OC'er. Yes, Afterburner does allow you to increase it further past the max clocks if you enable UNOFFICIAL overclocking. You already know this but I'll say it again, be careful when tweaking the voltages and such, and remember to take SMALL steps increasing the voltage ( I MEAN TINY).
If you choose to go the unofficial OC'ing route, then you most probably will have to increase your voltage, as the stock voltage probably won't support much more OC'ing than you've already achieved (I may be wrong, since I don't one a 7850, but that's how it is with my 5770)