Why do you ask?
Are you contemplating a change from what to what?
I suspect that if you are planning to upgrade from one GTX670 to two, the answer is no.
As a rule, the graphics configuration is mote important than the cpu. Depending , of course on the game.
Your i7-920 is a competent cpu chip, and it can be overclocked easily.
To help clarify your options, run these two tests:
a) 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.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 50%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
set to 50% and see how you do.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.
Another way to do this test is to OC a bit and see if your FPS increases, indicating that the cpu is a limiting factor.
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.