It's 612MHz so I am pretty sure it will be slower than 6990, albeit at ranges of 5-10%. What I heard puts it miles ahead of 6990 when it comes to noise, however.

If it was similarly priced to 6990 it could be a choice that's as good as the 6990, but anything more expensive is quite dumb.

The 6990 by itself isn't a very good buy either. So I'd say keep clear of dual-GPUs this generation, and if you need something faster than a 6970 or 580 (can't guess why you would, if you're not running multiple monitors), go with 6950CF or 6970CF.