You can check this review for Crossfire performance:
http://widescreengamingforum.com/wiki/ATI_Radeon_5870_Eyefinity6_-_Featured_Review
It's of the E6 edition but if you look at Anandtech's E6 review there's no performance difference on 3 monitor configs. You may have to give up some IQ even on a Crossfire setup but to me the immersion is worth it.
Ouch, Batman and STALKER CoP lay waste to a 5970 @ 5760x1200. Doesn't look good for my 1Gb rig. I like 30FPS mins not averages.
Thank you for the link.
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