The cooling capacity will increase a bit with more air flow thru the radiator, yes. But how hot is your OC'ed CPU that that huge liq. cooler isn't doing the job?
And remember, more fans = more noise. Of course with 4 fans you can lower the RPM to reduce noise and still have sufficient air flow. But then you may be back to square one again. Check out the Linus video about that sort of issue: https://www.youtube.com/watch?v=UyC3lZ5WFMk