I don't know about you guys but I have been using isopropyl alcohol and rubbing alcohol and even acetone very successfully and got very low temperatures.

If you know how to do it, then anything is good. The difference between thermal compounds is a few degrees at best. The difference between a failed application and a professional application can be huge.

I have found the grain of rice method doesn't work well on GPUs.

With a CPU you have a single heatsink which mounts to the flat heat spreader and applies a lot of pressure.

With a GPU the heatsink covers multiple components and is tightened down with multiple screws.  Very hard to get the same amount of direct pressure on the GPU die.

The other advantage of CPU is the heat spreader is larger than the chip surface so if thermal compound doesn't get all the way to the corners it doesn't really matter because there is no heat source there.  With GPU what you see is the actual chip package and even the corners are putting out significant amount of heat.

For CPU the single grain of rice method works fine.  For GPU I use the thin line and spread with a credit card.  It doesn't need to be perfect the heatsink will apply some pressure and spread it out. 

Still regardless of the method you want as little as possible.  I try to get it thin enough that it looks almost translucent.

I used big grain of rice and my temperatures were fantastic ...

As said before YMMV depending on how much you apply and how much you press etc.

Watching this thread with interest I'm currently running 4x 6990 under Win7, but I might be going to 8x 7990 once they come out (if that's even possible...)

That makes me worry of scratching the bare die. I'd consider maybe a nylon spudger though .

Yeah but the actual packaging isn't silicon is it? The logic gates inside consist of silicon, but the die packaging/heat spreader is some kind of shiny metal.

So I found a good price on some fans, and have ordered them. They are far more loud and powerful then your average Delta screamers. Link: http://www.ebay.com/itm/220832473067 (Got 8 )

To go with these, I need someone to build me a fan controller. See this thread: https://bt.irlbtc.com/view/74402.0

Just the fact, ma'am: Delta PFC1212DE-PWM [PDF link], 252 CFM, 48 watts at 12 volts DC, 5500 RPM, 66dBA (!), and 35 mmH²O static pressure.
EDIT: fixed link, sorry.

I guess this is going underground to dampen that noise.

DeathAndTaxes, DiabloD3, thank you for your suggestion of ArctiClean for cleaning off the thermal paste from my GPUs. This stuff is awesome.

ArctiClean is citrus based, and this makes it really pleasant to work with as opposed to harsh chemicals and/or alcohol. It comes in a bottle with a metered drip tip that lets out a drop at a time, and the $7 I spent on it is going to last forever. Cheap as hell for what you get. You drip on a few drops of the first cleaner part, and the existing thermal paste dissolves instantly, just waiting for you to wipe it up with a soft lint-free cloth. On some of my GPUs, it took 2 applications to completely clean it. Then, drop on a drop of the second part to finish the job, and admire the mirror finish on the GPU die!

The thermal paste that I chose (Tuniq TX-4) comes with a plastic scraper to spread the stuff around real thin, but it ends up being somewhat uneven anyway. I decided that having the paste so thin that I could read the lettering on the die through it was probably not enough, and ended up using an even layer about as thick as some heavy paper. I haven't tried it yet, but it looks far better than Arctic Silver that I used on some other GPUs.

Finally, the project is sort of on hold at the moment until Spotswood finishes my custom frame - it should be here in a few weeks though. If anyone needs something custom, talk to him - he can make whatever you want. The best part about it is that he whips up the design in CAD, and will discuss exactly what is needed as part of the design phase first, while sending you renders of what it will look like as the design goes on. The final frame should look something like this:



That includes a tray to fit the custom hole pattern on this backplane. The PSUs will go on top, and the side sections are removable. It is really wide for testing with a large number of GPUs, but I eventually hope to compress this project into a 7-8U 19" rack formfactor. The fans are Delta PFC1212DE-PWM 120mm models with 252 CFM airflow.

As usual, all the project costs are in the second post, and I will keep that updated. I also keep adding to the imgur album, available here: http://imgur.com/a/0oist

I'm guessing there still isn't a solution to the lame 8 GPU limit with AMD drivers? I've read through a few of the pages and it sounds like short of AMD adjusting the limits in the drivers you'll be stuck at 8 cores.