Do extra 6950 shaders matter?

[amazingrando]

There has been a lot of discussion about unlocking the extra shaders on the 6950.  I was wondering what people have seen in the real world for a performance boost?

Wondering if it is better to
1) go with a reference card that you can unlock but might be limited in OC?
-or-
2) go with non-reference card that OC's really well (e.g. Gigabyte 6950 OC) but not unlock?

With my Gigabyte 6950OC running at 900Mhz I get about 366Mh/s now.  I am buying a dozen more GPUs and would really like to stably do 400Mh/s or better

[1714079102]

1714079102

[Miner99er]

Difference of between 330-370 Mhash/sec to 410-440Mhash/sec.

[amazingrando]

I'm going to try to unlock one of my 6950's.  Going from 366->400+ would be a nice boost, especially since it doesn't increase power consumption like OC'ing does.

[Jack of Diamonds]

It's worth the near-zero risk of bricking the card, you gain in the best case 40-50mhash/s more. Worst case the extra cores are defective, you lose nothing.

Really, if you have a 2gb model they even have a dual bios switch, you can't screw up in any way (even if the flash went bad, just switch back to bios1 and try again)

Anyone can do it and it's safe.

[deslok]

One thing to keep in mind is that those shaders may be unstable they are locked from the binning process(just like intel and nvidia use on their own chips) either for defects found or to adjust supply. If you plan on doing it read through a cards reviews and see if people are reporting success on it odds are you'll see a few that failed as well on any card so it's not a guaranteed thing although it is as jack points out worth the attempt just don't plan on it always working.

[kano]

I'm going to try to unlock one of my 6950's.  Going from 366->400+ would be a nice boost, especially since it doesn't increase power consumption like OC'ing does.

So how did that go?
I've got 2 GA HD6950's (1GB) and certainly would be interested in knowing what happened!
(Edit: and of course what you used to do it - mine are on a xubuntu USB box)

[amazingrando]

Ok, so I spent many hours last night trying to do the unlock.  Here is what I did

1) First I did the chewing gum mod (http://hardforum.com/showthread.php?p=1037522585) but adapted to the Gigabyte 6950 (http://www.techpowerup.com/forums/showthread.php?t=148806).
2) The gum mod worked and allowed me to write to the bios
3) Used GPU-z to save stock bios image
4) Used RBE to edit the bios and unlock extra cores
5) Flashed bios back to the card
6) Rebooted
7) Result= no change in number of shaders

Tried again with Wizzard's script for modding the bios image, also no success

After reading in some other forums it appears that ATI/AMD have gotten annoyed that users can reflash and unlock more shaders.  Thus, they have started to laser cut connections to the extra shaders on the die, making it impossible to unlock.  This appears to apply to all recent dies.  

I am running Ubuntu 11.04 for my mining rigs, but RBE is window only so I took a spare drive and installed Windows 7 to do this.  Tools used were GPU-z, Radeon BIOS Editor (RBE), ATIwinFlash, and Wizzard's mod script (sometimes works better than RBE)