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Is the only reason for doing this to lower temp? Or is it true that it increases mhash?

I can't do it in Afterburner anyway, if I try to set it to a lower mem clock it and apply it, it doesn't actually apply, it just shows stock speed in the afterburner graph.

Is it worth it for me to go through all that trouble to lower mem speed?

It also lowers power consumption a bit. The core clock can also affect how much you can lower the mem clock without degrading performance.

Example, my 6870 performs almost the same at 300-350, 600-650, 950-1050. Default TDP is around 151w, by overclocking the core, power consumption will increase by about 25-30w especially if you also increase the voltage. By lowering mem clocks, the power consumed wont be as much. Lets say, power consumed is 20w lower, I pay about $0.2 per kw, that will be $2.88 a month savings. Imagine the savings if you have multiple rigs with multiple gpus.

Most DDR5 cards is comfortable with 300-350 mem clocks (according to my 6870 and 5670), DDR3 and DDR2 cards perform well at 250 mem (according to my 4850 and 4650). Of course, cards working at 100% utilization lives longer at lower temps and wont wear out your fans fast and your ears will thank you for the lower fan noise.

In short:
1. Lower temps
2. Lower power consumption
3. Lower noise levels
4. Can also help in achieving a little bit higher core clocks

Lowering memory clocks to 300 increases the hashing speed of all 13 of my cards (5850's and 5830's)

I would say it is worth it if you can get them to hash faster.

Hmm then how do you do it? I can't do it on Afterburner, the lowest is 625 on my 6990 and it doesn't let me set it as that anyway.

There's a trick to bypass the limits in afterburner.  Here is a guide to doing it.  After you do it, it should allow you to underclock and overclock past previous limits.

http://bitclockers.com/forums/index.php?topic=5.0

I tried that and it would freeze up immediately when I opened Afterburner.

what card are you using ?

What do you guys recommend for a Radeon HD 6950? 1 GB GDDR5 Memory?

Same here, except with 2 gb

Memory size doesn't matter. You'll probably be using a couple of MBs of it.

Thanks, thatt didn't answer our question...

Yes it did. The question was, "What do you guys recommend for a Radeon HD 6950? 1 GB GDDR5 Memory?"

My answer was that 1 GB GDDR5 or 2 GB GDDR5, it makes no difference mining-wise. That's the right answer for that question. Now if the question you're trying to ask is:

"What settings should I use for a 6950?"

then you will get a different answer. Start with one of the settings listed here (https://en.bitcoin.it/wiki/Mining_hardware_comparison) and play around with the settings until you find what works best.

Anyone know a program that can handle these, Sapphire brand?  MSI afterburner doesn't support, won't even start with these cards.  Trixx only allows 1 of 4 cards to be tweaked. 

to lower beyond spec i have found the only way is to use RBE and edit the bios files, ive tried the other 11.6 version changes etc, but its been unreliable across all my cards.

Anyone knows why I'm getting messed up artifacts in the afterburner windows after setting mem clocks to anything below 400? The artifacts come with load, as soon as I start the miners they show up, nothing when the cards are idle.

BTW my second, exactly the same machine doesn't have this problem.

My experience show that some cards (including mine) are not stable at 400 memory, so you better run it at 300 or 500, 600.
To the author of the thread, if are using single card, go for saphire trixx :)

Install Rivatuner (the old progie which Afterburner was based on), then use RBE (no need to modify or flash bios) to make Rivatuner work with your 5000 and 6000 series cards. You can also modify the clocks of your other gpus of your multi-gpu system. Unfortunately, Rivatuner can only lower your mem clocks to half of the default clocks. But you can trick Rivatuner to lower the mem clock of your primary card even more by using afterburner or trixx first to lower mem clock then exit, open Rivatuner, detect clocks and Rivatuner will see the lower clock as default. Enable "Apply overclocking at windows startup". Make sure afterburner and trixx are not loaded at windows startup.

Trixx just updated.. due to mining (http://forum.bitcoin.org/index.php?topic=28335.msg356433#msg356433)

the new version supports multiple cards.