Hi Qlik Ranger,
If we isolate your hardware in this question it is an Intel E7-8800 chipset architecture which I would advise against.
The E7-8800 is particularly aimed at eight socket(CPU) architecture that introduced unfavourable inter CPU communication over QPI links. Much as I explained in my post below.
If you are only using a single CPU this should be less of a concern for now, but will be terrible once you add more CPUs to the server. If you are already on multiple CPUs changing the chipset is highly likely to be beneficial.
The alternatives are either a recommended server based on E5-2600 or E7-4800.
As you mention the upgrade to E7-8870 will not give that much of an increase.
Switching to non low power would be ideal and recommended, but it's impossible to state how much the improvement will be. I'd expect a bigger improvement from the change of chipset to E5-2600 or E7-4800.
This was only a brief comment on the hardware.
Two other massive factors come into play as well: Usage pattern (how many users, what do they select etc..) and Application design (Expressions, data model etc..)