Because I am a hardcore fan of 3D video games (PC), I know something about video cards. I really like to share it with people here. Personally, I like nVidia cards (ATI guys, don't be nervous, I just said "PERSONALLY") because I had bad experiences with ATI drivers before. And ATI driver is still a big problem all the time. You may think driver is not important, I will tell you it is wrong. Driver serves as the connection between raw hardware and all other software (DirectX for example) that uses the hardware. A bad driver could make the performance of the hardware down to 50%. You may think you've bought a powerful monster, and then the bad driver makes it a dwarf. That happens.

Ok, anyway, let's back to nVidia cards. The newest series is the 7 series. I only care about the high end cards or 7900 and 7950 series. If you want to buy any card(s) in that catagory, here is the list of cards sorted by

performance:

2x 7900 GTX(GTO) in SLI >

7950 GX2 > 

2x 7950 GT in SLI  7900 = 2x 7900 GT in SLI >

 2x 7900 GS in SLI >

7900 GTX (GTO) >

7950 GT >

7900 GT>

7900 GS

price (listing price, you can always find cheaper ones here at eBay):

7950 GX2 ~ 500$

7900 GTX ~ 400$

7950 GT, 7900 GT ~350$

7900 GTO ~ 300$

7900 GS ~ 250$

Best Bang for the Buck

To combine performance and price, you will find 7900 GTO is the best one. That's why I bought one at home to replace my old 7800 GT OC. As you may know, it is a new product released 2 weeks ago and immediately sold out all over the internet. Why? Because it is actually a 7900 GTX which usually sold for 400$! Mine is even shipped to me with a 7900 GTX's box with a "GTO" sticker on it. The only difference is the memory's clock has been down tuned to 1320MHz (somtimes 1200MHz). But it is very easy to tune it back to GTX's 1600MHz using NVTweak (google NVTweak, first entry ). When you install the NVTweak, it enables the hidden overclock functions of your nvidia driver. Then you can easily slide the memory clock bar from 660MHz (or 600MHz) to 800MHz. The memory data clock actually is 2 times that frequency which will be 1600MHz then.

After I bought my GTO, the first thing I did is up-clock it to GTX setting. I should say it is not an over-clock, it is an un-do of the down-clock done by the manufacturer. So the performance? Excellent, same as GTX. Stability? Super stable. My card can run Battlefield 2142, Battlfiled 2, Faces of War, Rome: Total War, Halflife 2: Episode 1, Ghost Recon: Advanced Warrior for 2 week without a single problem.

SLI

If you want to go SLI, your cheapest choice will be 7900 GS. Single GS card is weak, but if you get 2 and SLI them, it can beat any single 79xx card (7950 GX2 is not considered as a single card). Here in eBay, 2 standard quality (almost not possible to overclock) 7900 GS can be found quite cheap. I almost got a pair of used ones for 270$ (out-bid by someone else only slightly). But to run SLI, you have to have motherboard support which is not always true for everyone. A single GTX or GTO is within 10% -20 % of 2x 7900 GS, so I bought 7900 GTO.

With the new release of GTO, finally 2x GTO(GTX) in SLI becomes affordable. The performance will be the best you can get. I almost did that but my power supply only provide 520W max and 2x GTO requires 550W, so I give up.

If you don't have SLI mainboard and only have one PCI-E slot, 7950 GX2 will be the only choice to maximize performance. 7950 GX2, if you look at the card, is 2 downclocked 7900 GTX stick together (instead of 650MHz GPU, both are at 500MHz). You may think of up-clocking it back to 650MHz, but I tell you it is almost impossible. Why? Look at the fansink of 7900 GTX (GTO), it is HUGE! Actually the fansink itself may cost 50$. But when nVidia stick two together, to save space they have to down-grade the fansink to GT's level. With that kind of cooling device, upclocking anywhere higher than 500MHz will be unstable. And you can hardly install your own fansink to 7950 GX2. nVidia still carefully made 7950 GX2 more powerful than 2x 7900GT or 7950GT in SLI so that it can cover its price range without competing their own cards.

Overclock

With NVTweak, over clock is just to slide a sliding bar. Just that easy. 2 things affect the overclock capability: the quality of the chip and the quality of the cooling device (fansink). From various sources, the best overclock card will be 7900 GT or 7950 GT. Some special edition of the card (like the eVGA signature series) can be overclocked higher than GTX (from 450MHz to 650 MHz). That's a huge jump! But not all cards can achieve that and the eVGA signature series is not cheap at all! Usually, overclock it to 500MHz is safe, anywhere higher depends on individual card.

7900GTX(GTO) has excellent fansink, people have successfully overclock it to 710MHz (from 650MHz) with the stock fan and to 810MHz with water cooling. One interesting thing is in some GTO cards, there is a resistor to prevent any higher than 1600MHz frequency for memory. People are still seeking ways to overcome that resistor which is designed to maintain stability of the card to achieve higher performance.

Conclusion

If you want best performance with least money, 7900 GTO is the choice. If you have SLI motherboard and a decent PSU (power supply), 2 7900 GS may be a good choice too. But keep in mind that a game's performance is not solely determined by your graphics card: your CPU and memory also matter. If you installed NVTweak, it can tell you the frequency of your GPU, memory, frame/second and core temperature. If you found the FPS (frames per second) is low and the core temperature is also low. That means somewhere other than the GPU makes your game slow. If you found your core temperature is very high, that means GPU is working at full strength, the bottleneck is GPU for sure. Then you can choose wisely which component you should upgrade.