Comparing the dual graphics platforms remains difficult these days, because the differences are as large as they can possibly be. This does not refer to overall system performance, though.
Due to the memory controller that is integrated into AMD's current processor families, the effective performance difference between various AMD platforms is at best very small; it may even be negligible. Using business or multimedia applications or CPU-intensive software, we found no performance difference that would make either platforms the clearly better choice.
Graphics performance is a different story, tough. In theory, the nForce4 SLI X16 chipset is the better choice for demanding graphics platforms today, since it offers full x16 PCI Express bandwidth (4 GB/s up and downstream) for each graphics board. However, there is not much software around that could possibly benefit from this, and most of the graphics data is processed within the local graphics frame buffer anyway.
The next logical step is to compare dual graphics performance, since this is what both ATI's Radeon Xpress 200 Crossfire Edition and NVIDIA's nForce4 SLI chipset family were designed for. On the one hand, ATI has not yet delivered its Radeon X1800 Master cards, which are essential for challenging NVIDIA's successful GeForce 7 series in the prestigious dual graphics arena. On the other hand, we would not want to take a step back and pick GeForce 6 series cards for dual graphics comparison. After all, would anyone who is into the latest toys buy previous-generation products? We don't think so, which is why we chose the GeForce 7800 GT series for our SLI benchmarking session; it represents the entry level for the 7 series.
For the sake of fair play we decided to cross-benchmark both platforms with graphics cards from both ATI and NVIDIA. While we don't believe that either of the two players would implement pitfalls in its drivers to make the opponent's graphics technology look bad on their own platform, there is still a chance that an ATI platform with ATI graphics or an NVIDIA platform with NVIDIA graphics could run better than with mixed manufacturers. Luckily, this is not the case.
At the end of the day, the graphics battle is still undecided, and it is likely going to remain this way. Getting an SLI system is the best choice from a graphics point of view today, but the whole situation will turn around as soon as ATI gets the chance to regain the graphics crown - assuming it doesn't screw things up, of course! Unless both players allow support for both dual graphics technologies on their own platforms, the customer will always be bound to one particular company, which we don't believe is the right way.
The feature analysis is pretty simple. NVIDIA offers more connectivity options due to its integrated Gigabit Ethernet controller. It also offers the better feature set by supporting the latest mass storage features, an integrated hardware-assisted networking firewall, and more elaborate software.
ATI, in turn, is capable of scaling its Crossfire Edition Radeon Xpress chipset all the way from the high-end to the lower mainstream thanks to flexible south bridge choices and third-party networking chips for GbE. An entry-level Crossfire system could consist of an older ATI SB400 or SB450 south bridge and 100 MBit integrated Ethernet, while ULi's M1575 and a Gigabit Ethernet part for PCI Express remains the best choice for premium users. Still, it won't be able to match NVIDIA's higher PCI Express lane count.