You can run them in trifire but I am concerned about going with AMD on this build. I don't think 3.8ghz would be enough to keep them from bottlenecking at 1920x1200 res or below. Maybe at 2560x1600 or if you are going to use three or more monitors in eyefinity the bottleneck would move to the video cards.
Try to get that processor as far above 4ghz as possible or better yet if you haven't bought your motherboard yet you might want to change over to Intel and Sandybridge processors. They get to 4.5ghz and above pretty regularly from all the reviews I have read.
My freind has two brand new ones that he couldnt use since he got a DOA 990x processor so hes selling them to me for $150 each, i currently have 1 Hd 5870 eyefinnity 6 edition. i run it at 5760x1080. i have a AMD phenom II x4 955 @ 4.0ghz right now with a biostar ta890fxe. i could easily go to sandy bridge if i needed to, i havent bought the other motherboard yet, if i was to go to sandy bridge, could someone recommend a motherboard and cpu that preferably wont break the bank? and has the ability to have trifire?
AMD phenom II x4 955 @ 4.0ghz
4gb DDR3 1600 patriot g series sector 5
Biostar TA890FXE Motherboard
Sapphire Hd 5870 2gb Eyefinity 6 edition
Rosewill 750w extreme series psu
1TB western digital black edition
250gb seagate barracuda (running SRCDS)
32gb Corsair V32 SSD
Intel Sandy bridge Processor
Intel 1155 socket motherboard capable of trifire
Corsair 1200x power supply
3x Sapphire HD 5870 2gb Eyefinity 6 edition
I looked at all the three slot (pcie) motherboards at newegg and I don't like how the bottom slot blocks all of the different ports along the bottom of the board if you use a card with a double slot cooler. I would go up to a 4 slot (pcie) motherboard.
I like the layout of the Asus P8P67 WS Revolution motherboard.
As for the cpu I would have to have the 2600k. I know most people will say that the 2500k is all that you need but if you are going to spend that much money what's another $100 dollars between you and the egg? Also you would have the top of the line processor in that series. We all use our computers for more than just gaming and some of those extra features may come in handy!
I looked up your present motherboard and you can run x-fire on it. At that high res (5760x1080) a second card in x-fire should really be a huge improvement in fps. I wouldn't think that the cpu would be a bottleneck at that res.
I would buy one card and see how it scales before I would do a new Sandybridge build.