Actually, the i7 chips are available at 2.66 GHz,  2.93 GHz and 3.2 GHz, but yes the i7 920 is definitely more powerful than the Q6600. If you're going to be rendering in Cinema 4D, you may want to seriously consider the i7 920, because it is about 25-30 percent more powerful than the Q6600 in most benchmarks, and when you factor in that i7 chips now have hyperthreading (which Cinema 4D supports) and Core 2 chips don't, that's another 10-12% performance difference, which means render times in Cinema 4D are potentially almost cut in half by the i7 versus the Q6600. Benchmarks are showing that this is definitely the case.

http://www.behardware.com/articles/737-7/report-the-intel-core-i7-in-practice.html

Of course, DDR3 RAM and i7 compatible motherboards are a fair bit more expensive than a Core 2 Quad system with DDR2 RAM. It's up to you whether it's worth an extra $200-300 for a 40% reduction in render times.