Neither card is worth the price. Neither card is required to get acceptable framerates in today’s latest and greatest games.
IDK what you’ve been offered for the 5970 but when newegg stopped selling them they were around $600 and 6990 should be around $750.
If you actually care about what you’re throwing money at, you can get acceptable framerates, not the absolute BEST but still good enough to enjoy, with a $300 6950 or $200 GTX560.