Quad core processors are about bragging rights and offer little substance to the overall performance of the computer. Yes, you can find benchmarks which show a quad core CPU kicking a dual core all over the place. Of course, if running a benchmark is what you like to do, then I suppose a quad core CPU would be the thing to get. I prefer applications to run better than a benchmark myself.
Higher clocked dual core CPU's offer better bang for the buck.
The thing about high end systems today is they are very picky about power. The better quality the power is, the cooler they run and more stable as well. I have seen a lot of people spend a lot of money on their systems, only to go cheap on the power supply and they regret it.