Maximum PC

So a nice upcoming bonus at work, gets me in the mood to play "enthusiast" and think about upgrading my pc.
My Gaming Rig isnt even 2yrs old yet, with a asus sabertooth p67 board, i5 2500k running cool at 4.2 ghz, and a gtx 570 for the graphics.
It runs all the games i play fine at high settings Skyrim, D3, and Witcher 2, but what should i upgrade next?
Should i drop the p67 board, and get a flashy x79 board and go with Ivy Bridge?
or stick with Sandy Bridge and maybe a i7 2700k?
or perhaps drop another 570 for sli, or go with a 670
my power is more than capable with a cosair 1000w psu
I just wanna stay top notch, what would benefit me the most first?

Thanks all

The first upgrade in any gaming PC is usually the video card, because that's almost guaranteed to be the bottleneck first. In the direction games are going, a high-midrange to high-end processor in a gaming PC is viable for at least four years before an upgrade is absolutely needed. In fact, no game effectively uses more than two cores.

So I would drop another GTX 570. It's cheaper than the 670 (I think...) and you get more out of it.