|Going from a 7600GT to an 8600GT is not a worthwhile upgrade. Yes, the 8600GT is better, but not enough to justify the cost. If you're getting the card for free, go for it...if you're spending money for it, you're wasting your money. There are plenty of other cards that are substantially better in the same price range.|
Have a look at this chart from Tom's Hardware & note what it says: "I don’t recommend upgrading your graphics card unless the replacement card is at least three tiers higher. Otherwise, the upgrade is somewhat parallel and you may not notice a worthwhile difference in performance."
Going from a 7600GT to 8600GT is only a ONE tier upgrade at best. It may be no difference at all...it depends on the type of memory used on both cards. GDDR3/DDR3 always trumps GDDR2/DDR2.
You'd be much better off with a Radeon HD4670 with fast GDDR3 memory...the faster, the better.