We had the same thread like this before:
http://www.tomshardware.co.uk/forum/249833-15-force-8800-768mb-geforce-9800
EMP:
You could also compare the EVGA 9800GTX ($330) vs the EVGA 8800GTX ($340 before rebate, $290 after rebate) and honestly even if I wasn't going to cash the rebate for whatever reason I'd still pick the 8800GTX.
From what I understand OC'ing the G92 does not net you the same performance benefits as OC'ing the G80 core (At least that's what I'm led to believe by some of the comments of G92 owners in this forum). The other thing that worries me a little about OC'ing these cards (That may or may not be fixed with the 9800GTX) is the fact that there were some strange problem going with the memory I believe when it was OC'ed past 2000 that affected the longevity of the card.
For what is worth, the 9800GTX is no doubt a great card (No matter how you look at it, it's a rehashed 8800GTS G92), however the 8800GTX still feels like the better "high end" package to me if you get what I mean. One thing that cannot be denied is that you will need a PSU for the G80 core to feast on, because they are power hungry.
Me:
Definitely agreed, the 768MB memory of 8800GTX helps it to beat the 9800GTX in higher resolutions
From tomshardware review:
So come on, Nvidia. Is this really the best you can do 17 months after the 8800 GTX?
Nvidia GeForce 9800 GTX: A card that's almost as fast as the 8800 Ultra at a much lower price is a good thing. But a year and a half after the release of the GeForce 8 series, and even though AMD doesn't really have anything that can go head to head with this card, we'd have liked a little more punch to replace the 8800 GTX with (which is also now being sold for under $400). What we got instead was a card that's very noisy under load and limited by a stingy 512 MB of memory. These drawbacks are especially disappointing given that the 8800 GTS 512 MB is very similar and less expensive.
+ Performance close to that of the 8800 Ultra at half the price / Support for HybridPower (with compatible motherboards) - Noisy under load / Only 512 MB of memory / Not different enough from the 8800 GTS 512 MB, 8800 GTX and Ultra, although they're previous-generation cards and often less expensive