Ok, while I work my way through this thread, I thought I'd post the route I took (just last night).
From reading the various comments all over, I decided that messing with the memory is too volatile so I'll avoid doing so.
I opted to mod my original BIOS (saved from the card itself using GPU-Z 0.5.1) to have unlocked shaders only using the modder made by rui0317 & w1zzard
here.
I tried pushing the clocks up to 850MHz on the core with stock V, but then backed it down to the original 810MHz to see that if there's errors, it's the unlock, not the OC. I will keep it that way for 2 weeks.
To be able to OC beyond the 6950 CCC limits, I used MSI Afterburner 2.1.0 beta 7 & followed the instructions of the OP in
this thread.
(I only removed the limits because Afterburner now allows them to be removed whilst still maintaining PowerPlay profiles.)
I set my fan curve to be 25% @ 50°C, up to 80% @ 80°C and have so far had temps stay under 70°C.
What I now wonder is, assuming all goes well for the next 2 weeks with unlocked shaders, is it worth trying to bump the GPU to 880MHz like the 6970... and if so, does the GPU need the voltage also bumped from 1.1V to 1.175mV as is in the 6970?
If the voltage needs the bump, is it safe for the power regulation circuitry of the 6950?
I have a very limited budget ATM, so these considerations are crucial for me as I can't afford to mess up the card. It's safety is my first priority with regards to this sort of modding/OCing.