9800GTX+ Issues

Ok, so I finally got a 9800GTX+, but it isn't as good as I thought it would be, I can't even play Assassins Creed on medium without lag, while I've seen 8800GT's play it on high without lag, and I can barely play Crysis on mainstream/gamer. Also, it says that it is 512MB, but when I run GTA IV, the memory ristriction say like 450MB (I can't remember). My CPU is an AMD Phenom 9500 quad core @ 2.2GHZ default (I overclocked it to like 2.5GHz. I have 6GB RAM. And a PNY 9800GTX+. Somebody told me that my CPU is bottlenecking my GPU, but I doubt it. Is my graphics card broken? Because it is pretty ***. I have a 550W power supply which is enough. I'm really dissapointed because I bought the 9800GTX+ and a 550W power supply for over $350. Please help me I don't know what is wrong with it. Thanks in advance.

I don't think it's your CPU either. I could play Assassin's Creed on High settings with my 8800 GTS 512 (slightly slower than your 9800GTX+) without any problems. I had my Q6600 @ 3.2Ghz however, so it would beat out your CPU since you've got the original Phenom.

Anyhow, I don't think your problem is with your CPU. I'd agree with Maziar though, check your GPU drivers. nVidia had a release that specifically increased performance with Assassin's Creed quite a while back. If you're using the drivers that came on the disk with your GPU, you're way out of date.

Hi i was about to buy the 9800GTX but after reading this i am thinking is it really worth it? i just recently fitted a new PSU Hiperpower 580 watts and was thining of buying the 9800 GTX to upgrade my Powercolor ATI HD 4670 1 gig GPU, but is seems like i might be in for trouble, can you advise if i should go for it, the make of the 9800 GTX is ASUS? thanks, will appreciate quick response.