Conclusion
Thanks to its dual GPU architecture and high clock speeds, the GeForce 9800 GX2 is indeed the fastest single graphics card NVIDIA has ever created. Gamers looking for the ultimate in 3D performance, look no further, as the GeForce 9800 GX2 is as fast as one card gets right now: the card ran over 1.5X faster than the GeForce 8800 GTX/Ultra in most cases. At the same time however, due to the GeForce 9800 GX2's $600+ MSRP, buying two GeForce 8800 GTS 512MB cards and connecting them together for SLI is still technically the more cost effective upgrade: street prices on bone stock GeForce 8800 GTS 512MB cards generally start around $250 and go up from there.
Not everyone has an SLI motherboard though. Many enthusiasts are gaming happily away on non-SLI compatible chipsets from Intel, like the X38/X48, and P35 Bearlake chipsets, or Socket 939 users who are still happy with their nForce4 Ultra motherboards.
For these types of users, the GeForce 9800 GX2 is a very attractive high-end upgrade. It gives them the performance benefits of SLI, without having to consume two PCI Express graphics slots, which is the primary drawback of SLI.
For the gamer looking to upgrade to quad GPUs, the GeForce 9800 GX2 is a no-brainer. After all, as we just demonstrated with our overclocking results, with a little bit of OC'ing, the GeForce 9800 GX2 can be clocked to run faster than the GeForce 8800 GTS 512MB SLI setup. We are still curious to see how three GeForce 9800 GTX cards combined together for 3-Way SLI performs though.
This is the beauty of NVIDIA's current 3D graphics lineup. Whether you want one inexpensive card, one really high-end card, or perhaps you want two, three, or four GPUs, NVIDIA's got you covered. Sure, AMD supports this feature as well, but as we all know NVIDIA's GPUs are performing better than AMD's in DirectX 10 apps right now.
Which path you take is going to come down to your needs and budget. Penny pinchers will probably want to stick with the 9600 GT, 8800 GT, or at most the 8800 GTS 512MB and upgrade to 2-Way SLI as their needs and budget warrants it, while gamers who can afford it may want to opt for the 9800 GTX or 9800 GX2.