The Haswell CPUs are pre-overclocked. At stock, when under load, they will automatically PC about 12%
A stock 4670k runs at 3.4 Ghz and turbos up to 3.8 (12%) under load ....
when overclocked, you can take most to 4.4 Ghz (+16 %OC).
A stock 4770k runs at 3.5 Ghz and turbos up to 3.9 (11%) under load....
when overclocked, you can take most to 4.5 Ghz (15 %OC).
The 0.1 GHz difference you see between the 4670k and the 4770k made the 4670k the "gamers choice" as the general consensus was it wasn't worth $100 for an extra 0.1 GHz, hyperthreading and a lil better overclock ability.
This is all changed with this latest generation
A stock 4690k runs at 3.5 Ghz and turbos up to 3.9
A stock 4790k runs at 4.0 Ghz and turbos up to 4.4
Obviously, more gamers are ponying up the extra $100 this time around