I wish I had done some comparisons with Intel's P55 chipset. I made some comparisons to the X58 because the 890FX is AMD's top-end chipset, so why not compare with the X58, which is Intel's top-end chipset?
But the P55 has been an enthusiast favorite because it's (A) cheaper and (B) you don't lose anything noticeable in the way of real-world performance. P55 motherboards are also much closer in price to 890FX motherboards.
But a P55-based system has one severe limitation: there are only 24 PCI-E lanes available, 16 full-speed lanes from the Core i5 or i7 processor, and 8 half-speed lanes from the P55 PCH. A dual-card CrossFireX or SLI system doesn't suffer much from the x8 lanes allocated to each card (Tom's Hardware measured about a 4% performance hit), but things change when you add USB 3.0 and SATA 6Gbps to the mix, since these features require PCI-E lanes to connect them to the rest of the system. A P55's limited number of lanes means you'll get either slower performance (using the half-speed P55 lanes) or have to "steal" some high-speed lanes from the processor, potentially slowing your graphics cards.
How much slower? I tested this in my review of ASUS' H55-based P7H55D-M Evo motherboard
. Using the half-speed PCI-E lanes can severely constrain USB 3.0 performance, depending on the device you're connecting. I don't have any data on motherboards that steal native PCI-E lanes for SATA 6GBps connectivity, though.
Very high end P55 boards like the ASUS Maximus III Extreme use NVIDIA's NF200 bridge chips to add another 16 full-speed PCI-E lanes (at the cost of a few clocks of latency). You'll pay for this feature, though-- the Maximus III Extreme is a $350 motherboard.
All of this is just a long-winded way of saying the 890FX chipset's extra PCI-E lanes confer a real competitive advantage, given that you can run triple ATI video cards and
USB 3.0 devices and
SATA 6Gbps without having to worry about anything. Given that video cards have a greater impact on gaming performance than CPUs, an 890FX-based system becomes very appealing for gamers: not only can the 890FX support triple-card CrossFireX while the P55 is limited to two cards, even running those three cards won't result in any slowdowns to other parts of the system-- you never have to worry about PCI-E allocation.
Something to think about...