ATI HD 5870 Scaling Performance: X58 vs P55 Showdown

Good read:

That said, if you are running a single card such as the HD 5870, either platform is fine. However, performance in x8 mode was a bit disappointing for those needing the second slot for purposes other than graphics. In the end, performance in games was still very good and only a benchmark would inform you of less than stellar performance. What we cannot answer right now is if the dual x8 PCIe capability on Lynnfield will become a true bottleneck with the GPUs that follow the current/planned releases from AMD/Nvidia.

So our conclusion still has not changed from a month ago, if you plan on purchasing a high end multi-GPU setup you'll want to go with X58/Bloomfield for the best possible performance. If you want a great combination of application and gaming performance without the power consumption or heat concerns, the Lynnfield platform is a very attractive alternative.
While the 1366 has 2x the available bandwidth (2xPCIe x16 v2.0) of the 1156 which would likely mean the 1156 won't handle too much beyond a 2x HD5870 setup, it's already been shown that even the best CPU's require overclocking at times to prevent being a bottleneck.

RAM, too can be a bottleneck and the top speed RAM is very expensive today.

So if you build a high-end system and then decide in two years to get the latest graphics card you'll also likely need a new CPU and faster RAM (and very possibly your Power Supply too). In this scenario, the only crucial feature we haven't upgraded is the motherboard. There's a pretty good chance that a feature like LucidLogix' upcoming chip which eliminates normal SLI/Crossfire limitations and just remaps the instructions will be a common part of motherboards.

So I just don't see the graphics bandwidth being that big of a deal. In my opinion by the time you need to upgrade your system you might as well buy a whole new computer. And by the time you do that, the next-gen consoles like the PS4 should be starting to kill the PC game market if you believe (and I do) a lot of the talk from game developers about the costs of developing for the PC. All they need to convert me over is support for Keyboard and Mouse and video scaled to either HDTV or close-up monitor proportions.

I'm thinking carefully about my next PC as I suspect it's the last time I'll buy a PC for games.