Speed is always key or slow post pro... What type of shots?
These are all single CPU Xeon's. The Xeon only advantage over a single i7-xxx is with 2 or more CPU's. I would search for an i7 processor, and definitely not that Pentium unit. The most important item is the CPU. Try to get one with hyperthreading so you really end up with the equivalent of 8 cores. Typically the i7's are clocked faster than Xeons. Premiere Pro is a very CPU demanding software.
Two disadvantages of the Xeons:
1) (Usually) Significantly lower clock speeds compared to the i7's
2) Not easily overclockable
Also, the Xeons that are "recommended" by Puget Systems use a completely different - and far more expensive - socket, LGA 2011 v3, than your planned workstation. That recommendation does not apply at all to the lower-end Xeons (for example, that particular Xeon in your planned Dell workstation is little more than an i5-4590 with 2 MB more L3 cache than the i5 - 8 MB vs 6 MB).
In addition, like Bill stated, that "quad-core" Pentium in that laptop in your original post is actually slower than even a dual-core i3 mobile CPU, let alone an i7 CPU. This is because it is based on the inferior Atom CPU architecture instead of the Core CPU architecture.
And all of those workstations that you mentioned are all of older CPU generations and use lower-bandwidth DDR3 memory instead of the newer, higher-bandwidth DDR4 RAM.