Its a little variable, as the ratios between different sub-system performance differs a little from the 480, 570, etc. i.e. as you increase the clockspeed shader performance might increase beyond the 480 while pixel fillrate still lags behind, so which is faster would depend on what the game was heaviest in.
To absolutely match the stock GTX480 in every case you need ~830-840MHz on the 470, but this clock speed would be quite a bit faster in many cases at lower resolutions i.e 1680x.
~750MHz will match a stock GTX480 in many games at normal resolutions, moderate levels of AA but fall behind as you turn up the resolution/AA.
900MHz on the core would put you into stock GTX580 performance but you'd need 1.1v on the core and ideally uprated cooling over the reference design.