Nah, you'll do just fine, overclocking Black Edition CPU is a piece of cake, just ramp up the CPU multiplier and you instantly got a faster CPU.

My Crosshair II have 140W TDP limit as well, I could overclock to 4GHz stable no problem at all just by upping the multiplier to 20. Just make sure you keep everything cool especially the CPU voltage regulator and of course the CPU itself. Do some stress test like Prime95 with 4 threads or Orthos to determine the stability and maximum temperature