If you are set on SLI, you really should look at the new 750i and 780i boards. The 680i is getting a bit long in the tooth and the new chips where developed for the faster 1333 FSB CPUs. I know the Q6600 is only 1000 FSB, but who knows, you may want to upgrade in the future. All that being said, I agree with the others and unless you print your own money, or have a HUGE monitor, SLI is not all that hot of an investment.
ANTEC 900 / ASUS P5K / C2D E6750 / SAPPHIRE RADEON HD 6750 1 GB/ CORSAIR 620 HX / CORSAIR XMS 4GB DDR2 800 / SEAGATE 320 GB / LITE-ON 20X DVD BURNER / WINDOWS 7 PROFESSIONAL / LOGITECH MX 518 MOUSE / SAITEK ECLIPSE KEYBOARD / ACER 22” WS LCD