Which Radeon 6950's are Unlockable??

Yes, it HAS to be a 2gb version. There are no 1GB 6970, so if you flash a 2gb rom into a 1gb 6950, you'll be in trouble.

I bought a 6950, 2 GB version, flashed it in 1st day and never went back. Go or it, you can't go wrong.

Do all 6950's have dual bios switch?
Some XFX have dual some not.
It can be done with one BIOS but is risky because sometime the shaders are truly defective and when you flashback the original BIOS faulty ones are still active instead of the good ones.

Does it ACTUALLY have to be the 2gb version?
Yes

What vendors that you know have done this succesfully?
Any using the reference design and a dosis of luck.Search Online for a VGA bios deposit if you wanna doble check

I would do your research before doing this. I read somewhere that the newer batches of 6950's don't unlock.

it will be hard to find a card that unlocks now. your best bet is just to buy a cheap 6970 if you really want one.

unlocking was useful back when the hd 6950 was $320 and 6970 was $370. both card have dropped by about $70 since then

Alternatively, you can buy a high end 6950 and overclock the living *** out it to the point where it out paces a stock 6970.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

not to make you jelly, but here is my stable of unlocked 6950's  

http://img804.imageshack.us/img804/1637/photobhw.jpg

There are very few HD 6950s that are unlockable but you will barely find one.
The unlockable 6950s are reference designed cards, the market now is full of non-reference designed cards which doesn't have the Dual BIOS and unlocking it is a risk.

The only best option for you is the Sapphire Toxic HD 6950, it's faster than HD 6970 because it has the factory BIOS of HD 6970
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Here's a review of it
http://www.xbitlabs.com/articles/graphics/display/sapph...

When did you buy yours and from what vendor??

First of all, it doesn't have to be a 2GB 6950. You can just unlock shaders on it, it's safer that way, and it will perform the same as a 6970 with lower clocks...

What he said, and afterwards, you can use MSI afterburner to overclock them to 6970 levels and beyond.

That said, most cards these days are locked by the ROM or cut shaders. The most recent cards I've seen people have success with are the HIS 6950 IceQ turbos. Here is an old guide to unlocking, there may be better guides out there now. If you scroll to the last page, you'll see a couple success with that card, and 1 that failed (and after help, managed to get it back to unlocked status).

http://www.tomshardware.com/forum/316974-33-radeon-6950...

the sapphire 6950 toxic comes with the 6970 bios preloaded, flick the switch and bam, 6970 performance for less money, if it doesnt work (unlikely) just flip it back and overclock

That's what i said instead of taking the risk.

No much difference that GURU3d, TECHPOWERUP guides.
Using MSI Afterburner will overclock the Core & Memory clocks, Shader is unlocked.

Okay, I NEED to get a new ssd (M4 or vertex 3, alas another post...) but I was just about set to get two of these before reading this thread

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

But how after reading about the toxic 6950 that is in stock (thought when I read about it previously it was out of stock at newegg) I'd love some further thoughts about which one (two) to run. I want to run sli or crossfire for BF3. I keep reading that sli performs better than crossfire.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thanks.

the flashed 6950s are far better than two 560tis, especially at high resolution

The techpowerup guide is far different. It flashes a 6970 bios onto the card, which only works on reference cards. I am not familiar with the Guru3d guide.

Your Answer:
Matthew,

Glad to hear you were able to resolve the issue. The 790i is capable of running AMD cards in Crossfire. If you have any further questions please contact us again.

Regards,
EVGA

That's what I just received from EVGA. I think I'm going to go for the toxic 6950's with dual bios that unlock to a sort of 6970 with a flip of a switch.

Best PCIe Card For ~$530:
2 x Radeon HD 6950 2 GB in CrossFire (Check Prices)

Excellent 2560x1600 performance
2 x Radeon HD 6950 2 GB in CrossFire
Codename: "Cayman"
Process: 40 nm
Universal Shaders: 2816 (2 x 1408)
Texture Units: 176 (2 x 88)
ROPs: 64 (2 x 32)
Memory Bus: 256-bit
Core Speed MHz: 800
Memory Speed MHz: 1250 (5000 effective)
DirectX/Shader Model: DX 11/SM 5.0
Max TDP: 400 W (2 x 200 W)

100312-3SR Radeon HD...
Amazon.com
$264.99
TigerDirect
$269.99

Recent tests performed by our very own Thomas Soderstrom confirm that the Radeon HD 6900-series features vastly improved scaling performance in CrossFire compared to previous-generation boards. As such, a pair of these cards represents a realistic pinnacle for our recommendations. At $530, two Radeon HD 6950s handily beat the GeForce GTX 580, and even come very close to catching the pricier Radeon HD 6990 and GeForce GTX 590.

Read our full review of AMD's Radeon HD 6950 for more information on the card and its accompanying architecture.

***Thanks ilysaml for the information in the thread about the toxic card. I think I'm going to go with two of these thanks to your post. ***