PlatypusSetsulDepends on the "performance updates" by valve.a 4770k won't see any performance gain over a 4670k in any game, with the possible exception of battlefield 4, where hyperthreading can be used, and even then, its a nearly negligible performance gain. TF2 uses a 32bit client, so max 2 threads and 4gb(?) ram can be used.
I'm using a 4770K too (although with a 7970 GHZ) and on maxquality I'm usually getting stable 240 fps in 6s, some drops in HL and some random bad drops (worst I've had was 80) in pubs, because TF2 refuses to use more than 30% of the CPU. If I can fix the CPU usage problem I'll get 240fps constant, everywhere, all the time.
tl;dr
It'll destroy TF2, as much as it is possible after years of horrible updates.
For other games the GPU might be a bit of a bottleneck, especially on 120Hz (but you can always switch to 60Hz for demanding single player games e.g. Crysis 3).
Definitely won't get better fps, but for streaming and multi tasking the extra cores are really nice (though I've never used a 4570k irl for more than 5 minutes so I can't really comment on the real world difference)