Using 4 monitors on dual gtx 580 matrix platinum

I'm building up a new stock trading system, as I was loading up the old system.

I've been building computer systems since '78(!) - it's a lot easier now - no soldering of chips and placing springs under keys keyboards now! BTW - my first homebuilt, a DEC PDP-1103, cost as much as a new car! And that was with paper tape; I was able to upgrade 2 years later to dual 8" floppy drives (256K each) for $2,500! And 8K of memory was $500.....

Anyway, I've built many systems since then, but this is my first entry into gaming video cards, so having to boot up fast on some knowledge.

I want four monitors on this new system, (I have other monitors on other systems for redundancy).

This new system has:
MB: Asus P8 Z68-V Pro
VC: Asus GTX580 Matrix Platinum (this has 2 dvi outputs for 2 monitors)
PS: 1250 watts
HD: WD 2 x 2TB, 7200 RM
DVD: Asus Blu-ray
OS: Win 7 64 bit

Desire: Want to add another GTX580 card to get up to 4 monitors.

Question: I'm a little confused about the SLI interface if I add a 2nd GTX 580 board. I'm under the impression that I WOULD NOT connect the SLI between the two GTX580 boards, as it's my (limited) understanding that the SLI serves to double the processing ability to a single monitor. Since I would be using 4 independent monitors, I would leave this SLI not bridged.

Thanks!

SLi can be switched on and off from the Nvidia control panel and in SLi mode you could run three screens as one for your gaming purposes.

Yes but a pair of GTX580's would be somewhat overkill for that.

What OS are you using?

Oops, I'm having a blind day! I have been told that you can run any other card alongside your GTX580 with W7 or XP so any card with two DVI ports would do the job whether it be an ATi card or an Nvidia card.