Your overclocked Q6600 is around the same speed as Core i5 750 so I would look at the Core i5 2500K if you intend to overclock.
The new Intel processors can only be overclocked in any major way by using the multiplier and only the K series have a fully unlocked multiplier. The non-K Core i5 processors have a few extra multiplier settings due to Turbo Boost meaning you can enhance it somewhat.
If you want to overclock you need to get a P67 motherboard altogether the higher end Z68 is inbound. AMD Bulldozer is also being released in June if you can wait.
TBH,your Q6600 for a single card setup will not very limiting if it is for gaming.