When to upgrade my 2500k @ 4.2ghz is it worth it at the moment??

I don't think so. The 2500k runs all modern games well-especially when overclocked. Intel's new CPUs should be launching fairly soon and may be worth the wait. Unless you have a very high end GPU setup with high end screens, you can't really do better than your current i5 for gaming. The new CPUs may change that.