[jjeaff]

I think by the time you built up that dell system to match the custom rig, it will be much more expensive. ECC has no benefit here (for anyone really). And while you get more cores and cache with Xeon, the 6 core overclocked i7 with double the clock speed would surely outperform except in the most parallel of processing applications.

As for picking all the perfect components that work together, there are myriad of people and places online crowdsourcing and benchmarking the perfect configurations. I doubt Dell is putting much thought and testing into their configs beyond reliability and cost.