According to Intel’s recent plans, QX9770 at 3.2GHz in socket 775 remains to be the fastest chip that you will see from Intel in Q2 2008. Intel doesn’t feel threatened and it doesn’t want to clock more than the current 3.2GHz. In 45nm, even the Quad-core doesn’t get that hot, and we've already seen them overclock to 4.4GHz with good air cooling. There is definitely space for a higher clock.  

Intel clearly indicates that QX9770 and QX9775 will remain the fastest in Q2 and probably even Q3 2008, and the next generation high-performance quad-core will be Nehalem itself.

Intel is also well known for changing its roadmap on a weekly basis and in case of any miraculous release from AMD that can match 3.2GHz Yorkfield, Intel would be ready to launch 3.4 and probably even faster Core 2 Quad – Extreme CPU.

So, if you want the fastest until Q4 you can get 3.2GHz QX9770; but it will cost you a fortune.