i am in the step up program waiting on a gtx 680. finally found a evga gtx 680 in stock at newegg, but it is the superclocked. i know i can sli the none oc with the oc, but the question is oc the second to match the clock speeds or down clock the sc card to match the reference? i just want the smoothest performance...
 
also i saw (on the forums here) that you can flash the cards firmware to match the sc? if so will this void my warranty? thx in advance for the replys

I had a SC and vanilla SLId for a while.  I got the best results by determining the max OC settings for each card separately and then setting them individually in Afterburner (assume you can also set them individually in precision).
 
If you're going to synch settings, flashing both to the same bios is probably your best bet.  Not sure on the warranty v. bios question.

You should be able to get both of them to operate at SC speeds

Jacob, what is the best way to accomplish this?
 
I too have a reference card, and just received a SC to install as soon as my high flow brackets come in next week.

Use Precision to set the frequency offsets. Set your SC card as primary and fire up OC Scanner. Monitor Precision to see where the boost frequency lands at. Then repeat the process for your vanilla card. Determine the correct offset to get the boost frequency of the vanilla card up to the same value as the SC card. For example, say your SC card boosts to 1180 MHz and your vanilla card boosts to 1100 MHz. You can then add +80 offset to the vanilla and it should boost to 1180 MHz as well. Set the offset for your memory frequency to match the SC frequency as well. +100 MHz should bring your vanilla card up to the same memory frequency as the SC card. Finally SLI the cards and test stability in OC scanner.

you can most likely just oc the non oc card to oc speeds and you're good to go.