Member Avatar for oenone

CPU speeds aside, does anyone know which of these 2 setups would perform better?
1) Nforce 4 chipset, 2 6600GT's (SLI PCI Express)
2) Nforce 3 chipset 6800GT (AGP 8X)

Thanks for the help! (sorry for the double post by the way....)

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Short answer: for an AGP system the single GeForce 6800GT is the safer, usually-faster choice; two 6600GTs in SLI only beat it in certain, driver‑friendly, high‑resolution/AA situations and they bring more cost, heat and complication. This mirrors the real-world testing from the SLI previews—SLI helps most at high res/AA but it doesn’t magically double single‑card performance. (anandtech.com)

Why: the two cards are different animals. The 6600GT is a smaller NV43 part with fewer pixel/ROP resources and a narrower memory bus; the 6800GT is a higher‑spec NV4x part with noticeably more render hardware and memory bandwidth. That hardware delta is why a single 6800GT often wins versus a pair of 6600GTs unless the game/driver lets SLI scale well. (techpowerup.com)

Important gotchas to clear up (answers to points raised by and others): SLI does not sum video RAM — each card keeps its own framebuffer, so two 256MB cards do not present 512MB to the OS/app. SLI scaling is application‑ and driver‑dependent (sometimes large gains, sometimes little or none); early SLI also required specific motherboards/driver profiles and accepted tradeoffs in power, heat and stability. If wanting SLI you need an SLI‑capable board, a beefy PSU and tolerance for driver/profile quirks. (nvidia.custhelp.com)

PCIe vs AGP bandwidth: PCIe x16 (PCIe 1.x era) has higher theoretical bandwidth than AGP 8x, but real‑world gaming at the time was rarely limited by that link alone—more important were GPU resources, drivers and CPU bottlenecks (low resolutions can be CPU‑bound, reducing SLI gains). If staying on AGP (no SLI board available), buy the 6800GT; if building a new PCIe/SLI system and you plan to game at high resolutions with current/soon‑supported drivers, SLI 6600GT is an option — but only if you accept extra cost/complexity. (electronicdesign.com)

Practical pick: AGP box → 6800GT. New PCIe SLI build and willing to tune/upgrade → consider 2×6600GT but plan for an SLI board, stronger PSU, and to rely on driver profiles for best scaling.

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Member Avatar for rcrevolution

umm it makes it sound obvious that the 2 6600Gt's will work better due to the double power and better chipset, but I really don't know.

Nvidia should be coming out with a 6800Ultra pci-e soon

Member Avatar for oenone

umm it makes it sound obvious that the 2 6600Gt's will work better due to the double power and better chipset, but I really don't know.

I dunno, the 6800GT has twice as many pixel pipelines, and twice the bandwidth as the 6600GT models. Does anyone know for sure?

Member Avatar for rcrevolution

yes but pci-e is twice the speed of agp 8x, and your getting 512MB if the 6600Gts are 256Mb each. Personaly I would go with the X800XT, or 6800Ultra if Nvidia releases a pci-e model.

Member Avatar for oenone

6600GT doesn't come in 256mb... and as fast as SLI is I seriously doubt you can just double the specs of each card to find how effective it would be. Also, a PCI express connection certainly does not mean that the card will be twice as fast, it is referring to the amount of bandwidth, I believe. The reason I won't get an X800XT or an 6800 ultra is that the 6800GT is a much better deal than either, and I am pretty sure that SLI 6600GT's beat a 6800GT, but I am not sure. Does anyone know?

Member Avatar for Member #2466

theoretically the Nforce 4 would perform better. The PCI Express has more theoretical bandwidth than the AGP. However, nothing today can throttle it enough through the north and south bridge to make a significant difference.

Member Avatar for Catweazle

The 6800GT will outperform two SLI'd 6600GTs for most purposes. there are some situations where the SLI'd cards would outperform even a 6800 Ultra. I'd imagine that the SLI capable motherboards, when they appear, will be restrictively expensive anyway, so I'd go for the 6800GT AGP for now ;)

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