I'm genuinely curious, why is it your number one feature? I know that ECC provides error correction, but aside from server use, is it really that critical?
Memory errors are a significant cause [citation needed!] of system instability. If you want a reliable machine, even a desktop, that is going to keep working, then ECC is very useful.
If you've decided upon ECC as a must, then it would be great for a system builder tool to then show you options based upon that choice.
And for some high end use case you might want to be looking at xenon's or even dual xenon's.
I could see a big data or HPC developer wanting to have a desktop that used the same processor as the cluster they are writing for - mainly in the case where your tuning for max performance and want to able to develop using the same complier flags.
If you've decided upon ECC as a must, then it would be great for a system builder tool to then show you options based upon that choice.