Need Recommendations on a New Build

[scole of TSBT]

It seems that the HPs have a much better stock cooling solution over the Dells.

Eh, not really. Temps are comparable to the T5500. Just don't have to mess with a riser. Though the heatsink upgrade on the primary cpu keeps it nice and cool. The cpu on the riser gets as hot as the Z600 cpus. Avg 75C?.

I see is the smaller and slightly less efficient PSU (650W @ 85% vs 875W @ 88%). You might have trouble running a 7950/280 and you would certainly have failures with 7970/280X on this platform, but it has enough power for a mid-range AMD card or any newer Nvidia GPU up to GTX 980. For this reason I've been sticking with the Dell T5500 - I need somewhere to put my Tahiti cards!

You're correct, the Z600 PSU is a limitation. I power a GPU in one with a separate PSU.