Just thought I would update everyone of my plight with the 7990.
Stability wise, it's holding it's own, I have the odd lockup under load, but it has reduced considerably. I tried replacing the thermal paste on the gpu's to alleviate the temperature differences and it made zero difference (but it has coincided with the card acting more stable). Now that Afterburner can show stats in 64bit applications, I did a session of 3dmark and it got scary.
Click to see image, too large to place on here
It appears to get a fair few degree's hotter in 3dmark than it does in Heaven.
RMA hasn't gone tremendously well so far. After receiving my RMA number, I had to send an additional note to the RMA to ensure they got all the information recorded that they would need, which was not responded to for 2 weeks. Another message to them was then swiftly answered, but as it's so close to the christmas period and I don't want to be without a card over the christmas holidays. I will persevere with the problems until Christmas is done with and will then send it back.
As I said, changing the thermal paste has made no noticable differences to temperature in the slightest. The general stabillity of the card has improved tremendously though and it's no longer the headache it was. It's still annoying that I have to deal with it having spent £480 on it, but it's a lot more manageable now.
The main issue is definitely the temperature though. My concern is, these are the temps in the winter, in the summer it will be well beyond any means of controllability as I am in a room with no source of heating, so the ambient temperature is low. If you add 10+ degree's to the ambient temperature, there is no way on this earth I will be able to control the temperature. With a 29c difference in temps between gpu1 and gpu2, something has to be up with it, but I can't put my finger on it.
For reference, I have never seen gpu2 rise above 72c.
So for now, I am all about limiting fps in games as much as I can to try and keep the temperature under control. Not ideal, but it's better than having to use the onboard haswell chip over the christmas holidays. Hopefully I can get it all sorted after christmas and get to the worry free gaming, which is why I actually put this much money into a system for in the first place.
Sorry for the long post, you will be thankful when I can put this all to some (hopefully) satisfying conclusion, so you don't have to read my ramblings about it.