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I despise the dual cards technologies personally, I guess I don't run at that resolution though so its not a worry
nope i don't use AA..Do you use loads of AA ?
Because if that's the case, the problem that you going through might be the lack of memory more than a raw power.
Remember, xfire isn't going to make your 512card a 1GB one.
Either way, if you're struggling a lot with your settings it's definitely worth it, if it's just a slight bit I would give a go some volt modding and clocking the heck outta single card and see if that helps first.
as J.D said i know all about crossfire as i used it with 2x 2600 cards.I despise the dual cards technologies personally, I guess I don't run at that resolution though so its not a worry
heat isn't really a issue because my case as very good airflow also the right side is off so more heat can be let out. and the left side isn't fully on..i would think it would be fast but they do run pretty hot better getting 1 card like a 4890. sell yours sharpish put difference to 4890 or 275gtx