Gaming performance
The ASUS is able to take a clear lead over the Foxconn N570SM2AA in Far Cry, but spends the rest of benchmarks more or less neck and neck. Interestingly it is unable to separate itself even in the Splinter Cell 1920x1200 4xAA and 8xAF Multi GPU test, where the 590 SLI chipsets x16 + x16 PCIe lane configuration should show an advantage over the x8 + x8 of the '570 SLI.
Comparisons to the Sapphire PURE AM2RD580 are less relevant due to the difference in GPUs. In the multi-GPU test the X1900 CrossFire configuration is able to demolish the performance of the GeForce 7900GTXs in SLI, but elsewhere performance is fairly close suggesting other bottlenecks may be the limiting factor, especially in Quake 4, which is clearly CPU-limited.
Summary
Throughout testing the performance of the M2N32-SLI and N570SM2AA is consistently similar. This no doubt stems from NVIDIA's chipsets being derived from the same basic designs and then features being stripped away to make up the lower-end SKU. The M2N32-SLI only being able to gain any meaningful advantage in Far Cry, and that's probably down to the sound ASIC used.
The benchmarking results may be, for the most part, negligible, but a 200 per cent price increase isn't. There is, of course, more to it than that, with the nForce 590 SLI chipset giving extra SATA headers and dual Gigabit Ethernet, but from a performance perspective it doesn't paint a pretty picture.