Some. Newer titles use more than 4 threads, it's as simple as that really.
There will be points where any quad core will hold back performance in certain games.
Its fine to run a 580 or 1060 with an ivy/sandy i5, just don't expect much more fps than your currently getting.
You'll gain on graohucal quality simy because you'll be able to run stuff at higher settings with no fps drops from what you have now.
A 3470/3570 isn't worth upgrading from a 3330.
Look at an i7 2600,2600k,2700k,3770,3770k.