Windows 7: 2 AMD 6970 in Crossfire or AMD 6990

I am at the point I am ready to upgrade my GPU. I have the money and I am ready to make the leap. The GPUs I am looking to get are the following:

2 x MSI R6970 Lightning

or

DIAMOND 6990PE54G

I just want to know if I would be better off using 2 card instead of one due to the driver issues. Look at my system specs if you need to know anything about my build.

If this is going to be a final purchase I would likely side with the 6970's.
If there is any remote possibility of later crosfiring 2 6990's I would definitely go with them.
The primary difference I think here would mainly be future expansion, which would still be possible with the 6990 but not so much when you already have 2 6970's.

The performance will be relatively equal from what little I could find comparing the two scenarios online.
As always the single card will likely cause less heat in the case. It's the reason I've quit doing sli/crossfire myself.
The heat produced by two cards working overtime in such a tight space just never jived for me.

Despite really good airflow I was forced to take the side off my case and use a house fan when I was pushing sli in the past myself.
Otherwise the cards hovered dangerously close to shut off temps under stress.

Either or. Also if so inclined you can also Crossfire a 6970 with a 6990 for tri-fire,

My Case and CPU temps are great so I have alot of headroom to go before heat would become a issue.

I once had a 4870x2 with a 4850 in tri-fire for many years. Would my powersupply be good for a tri-fire with a 6970 with a 6990?

I would go for 6970 cfx without second thought. Though to be honest if you game at 1080p there is no need for a second high end gpu

All depends on what games you play and I plan to have this build to last me at least 3 years. I think that I am going to get 2 AMD 6970 and hope that the kext support for Mac OS X 10.7 come around soon.