Nothing is guaranteed when over clocking, I have a 4770k, which on average should over clock slightly better than a 4670k.
I got a aweful chip, and I can be stable at 4.5 with 1.32v.
I would put the money into a more powerful processor (i7). Games do use the extra cores, it will be more futureproof. I have yet to see an overclocked i5 outperform an i7 in heavy threaded tasks.