haswell isn't out yet, is it? even so since the gaming recommendation for intel is the i5 3570k i'd guess the i5 4570k? we can't really tell till the processors are released any how just save £200/equivalent in dollars. If you mean ivy bridge the i5 3570k is all you need for gaming
The Haswell Architecture hasn't yet been released.
When it does though, I think the 4670K will be more than enough.
If you want to just game(no Overclocking), a 4570 will still be more than you need for gaming.
It depends on the game though. If it taxes your GPU, only then will the minor difference show up.