+1 for what Damric said. They haven't dropped XFire support for that model card, I have x2 HD3870s in a system here and they work fine with every game I have here ( I don't play GW2 as it's not the type of game genre I do play ). A friend of mine has x2 HD4870s in XFire and he's still playing his games in XFire mode with them.
You could always drop a mail to AMD and ask if that game played on that card in XFire does in fact have a CAP profile for it etc .. but in answer to your question - yes XFire is still supported with the HD4870 in XFire. It's a new game which came out 8 days ago, so if the CAPs don't yet have it included, then it might be in the next set etc ..
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