I5 3570k or i5 3450 non-OC gaming build.

I'd say the 3450 and spend the difference on another component (GPU for instance)

If you ever run into a situation where you decide you want to OC you'll regret not having the 3570K, granted you're not interested now who knows in the long run.

How about the i5 3570? Its locked so you can't overclock it, and its about $10 cheaper than the i5 3570K

For 10$ only I'd go for the 3570K. Like mac_mac_attack said maybe you will not OC right now but you could want to in the future.
The 40$ difference between the CPU's on the original post is something but 10$?Just have one less drink on your next Friday night and you already got 10$

All of them are powerful enough to keep up with any modern graphics card on the market. If you're absolutely sure you don't want to overclock, get the 3450. The 3570K might get you bragging rights, but good enough is good enough.