Well, this is a freak system. You must be a freak then

Seriously, as per the recent Anandtech review of the single-board Dual-GPU 5970 (which is basically similar to your 5870SLI) - this power is COMPLETELY wasted on a single monitor even at resolutions of 2560x1600.
Unless you plan on running multiple 1920x1200 screens with Eyefinity, you are paying for power you can NOT possible realize in any game of the next two years. Because any single LCD screen will cap you at 60hz refresh rate, thus at a max of 60FPS, which you can easily get with a single 5870 in all current games.
AND you will generate twice the heat, twice the noise, AND have to deal with Crossfire conflicts for new games. Not to mention you are paying a lot of money extra.
You could easily throw out the Velociraptor (good choice for a mechanical HD, but damn hot and noisy) which in itself is not cheap, use that money and the money from the second HD5870 to buy a 256GB SSD (Corsair or Patriot). As a System and Game Drive, that would ROCK your world.
Or you could get a monitor upgrade for that amount of cash, unless you are already on something bigger than 24".
Seriously, I'm not telling you to get an SSD because I'm an SSD fanatic. I'm telling you to get an SSD because otherwise you have a VERY unbalanced build.
With a given budget X, care should always be taken to spend equal on GFX, CPU and if possible storage. With the i7 Triple Channel RAM and super fast PCI-Express speeds, your only and serious bottleneck will be the mechanical HD, even if it's a Raptor, unless you run it Raid 0 (which I don't see since you only have one Raptor).
Personally, I wanted a balanced system with no clear component bottleneck AND low noise/heat. You are oversizing the GFX component at the cost of heat, noise, storage and setup simplicity (Crossfire).
Sorry, I know I'm rambling a bit. I also know that sometimes we buy stuff because it's cool to have even if we're not really ever going to fully realize it's potential. I have a 400EUR Cougar Force Sensor upgrade even though I never every even programmed the Cougar with more than normal in-game commands. So I completely understand the "It's what I always wanted to have" point of view, but if you are looking at best-all around performance and enjoyment for a given budget, you are on the wrong track with that dual HD5870 setup.