2012 Mini i7 2.3 vs 2008 Mac Pro

Thunderbolt 1 is capable of carrying 4 PCIe Gen1 lanes (or x4.1). Thunderbolt 1 gives you about 50% bandwidth of TB2.

What Video card do you intend to use (in either machine)

The $300 2x2.8 Quad Core (8 cores) 2008 Mac pro I picked up a couple months ago is much snappier than my mini with everyday tasks, but I have not tried an eGPU approach. The MacPro will way out perform the mini+eGPU, given the same graphics card. Most noticeable while editing.

I think eGPUs only make sense if you want to only use one machine, like a laptop, for everything.

You may want to check some of the gaming forums for eGPU performance comparisons while waiting for someone with more direct knowledge jumps in here.

 

In actual CPU performance, my quad 2.3 Mini is nearly as fast as my 8 core 2.8 2008 Mac Pro for things like running Handbrake, for instance. I would expect the Mini to be significantly faster than a 2008 quad core Mac Pro.

 

That Mac Pro setup would smoke the Mini.

 

Couple of things to consider:

(1) that the mini will perform well at some tasks, as suggested by chrfr, might be related to it's CPU having Quicksync which is dedicated core for video trans-coding - therefore high performance in this area is not necessarily an indication that the CPU is more or less powerful than another, but given this is a video forum it may be important to you

(2) if cost is an issue, have you factored in the price of an eGPU enclosure

I don't pretend to know a lot about Mac Pro GPU compatibility but the three that you mention are not very expensive compared to the Thunderbolt eGPU enclosures I found online - it seems to me that with the new Nvidia Pascal series in the wild it might be worthwhile looking for a cheap GTX 970 or higher Maxwell for that Mac Pro instead of eGPU plus enclosure - OSX drivers are available from Nvidia

I did look into eGPU solution about 2 years ago for my son - he has a Late 2012 iMac loaded but the GPU is not very powerful and he needed better for rendering in Blender - there really weren't any decent options at the time so I ended up building a Linux based computer for him that he is very happy with (need to add a second GPU though - GTX 970 is probably twice as fast as the iMac and GUI is super smooth even with big projects but he wants better)

At least there are a couple of decent options available today for eGPU, but not necessarily cheap and they seem to be Thunderbolt 3, which I hope is backwards compatible if you pursue the eGPU path

 

Its possible that you'd get more responses and maybe even better ones on this type of hardware question within the macpro forum. https://forums.macrumors.com/forums/mac-pro.1/