Looking at overclocking my HD 6950.

Specifically, it's an Asus DirectCU II. It's not the newest toy for sure, but I don't want to push it so hard it damages the card. The clock is set to 810mhz by default, and I have an Accelero Xtreme III instead of the stock cooler. What kind of overclocks can I expect to get out of this thing? It's been a long time since I bothered to OC a video card, but I notice the auto-tune feature is gone now. What's a good way to do this manually?

Grab MSI Afterburner, that's the easy way these days.

Is it one of the 6950's that can be flashed to a 6970? Quite an easy way to get a performance boost...

+1 for MSI Afterburner

Using AB, Just keep bumping it up in small increments until your cooling solution or silicon runs out of talent

With that cooler I think you would be good to 1.215 or 1.225 , just keep an eye on temps

you should have a 10 year badge ?

My unlocked 6950 (on an Accelero XP) would run up to 910/1350 without too much voltage, but every card is different. Make sure you increase the power limit in Afterburner and just increase clocks gradually starting with the core.