Even touching the voltage within safe limits is fine on the Radeon 7850 cards, except for a few models that aren't worth buying for overclocking. Keeping it around 1.2V is almost always safe (sure, there are failures, but there aren't any more really than at stock, so it's not a good tool in an argument against overvolting). It's not until you do something more extreme where your card is in serious danger unless there are other problems such as a PSU with bad load handling and such.
Still to stay on the safe side, I wouldn't advertise overvolting to someone who has little to no experience with overclocking unless they are helped directly by someone who knows how its done safely.