I agree on the core 2 duo. Supposedly AMD is releasing another chip in the near future that will blow away the Duo's...but that's just life. Intel will counter, AMD will counter-counter, etc. Right now, tho, I'm partial to the Intels. If you really want to get a performance per dollar comparison on specific systems, go to
http://www.spec.org and look at the benchmarks for different systems out there (you can compare motherboard chipset/processor/RAM combinations). When I was doing more building of systems, I'd be hitting spec.org pretty much monthly, importing the results into Excel, and sorting on performance numbers...then comparing to pricewatch or my supplier price lists for comparable systems to get the most bang for the buck, flat out baller, and cheapest usable machine specs, depending on the clients' needs. I haven't done that in a while tho, cause it was a lot of work and I haven't built many systems for random people lately.