The PRO is equal to the Delux or premium P5K. Both good boards and since Abit seem to be moving there support away from the UK either will probably serve you just as well as the other.
I'd still take the IP-35 at the moment as ASUS support is truely rubbish but their quality is fantastic (as is ABIT's).
The dark raider is plenty good enough to overclock the Q6600 but will perhaps run hotter and not quite as safely as the PRO would for very high clocks. Something like 3.4GHz will be not trouble though