yes it would be fine for 2 x 470's. you will see more improvement in games than forking out for a new i7 2600k. If you really want to upgrade the cpu, just upgrade to a quad core i5 for your current motherboard.
1) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
2) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.
It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.
I presume we are talking about game performance here, and usually a graphics upgrade is most effective.
I say if you want to upgrade your CPU you're better of getting an i5 750 or i7 760 since you already have an LGA 1156 board. Of course I'm assuming you're board also supports crossfire and SLI ^_^. If that's the case then it's not worth it to buy a new board and 2500k.
Anyway, yeah you should see an increase by adding another GTX470.