My point is...
All good points.
I think the old maxim still holds, you want to maximise speed ? (a) Max out RAM (b) use the fastest disks possible, today that means SSD's and TB2, preferably in a RAID-0 configuration (a striped volume) as a minimum - before you get into the more esoteric configs. Buy a mac-pro by all means, just buy it for the right reasons – speed differences alone won't be one.
For photographers, the MPG tests all indicate that differences in processing speed will be outweighed by the above. For video/motion (which is really what the mac pro is aimed at) , see
this comment on MPG (extract below)
quote
Transcoding video with Quicktime player is a poor test of performance for many reasons, the largest being that, unlike most pro video apps (Avid Media Composer aside), it does not leverage GPU acceleration at all, and it's implementation of multi-threading is notoriously poor ...
Really, the best test if you want to appeal to pro users is to transcode from 4k RED Camera or Arri Alexa raw files into an intermediate codec such as Apple ProRes 4444 or Avid DNxHD 345x using an application like Davinci Reslove.
If you're not trying to appeal to a pro user, then do the same test to ProRes 422 HQ using Final Cut Pro X or Compressor, which is a common workflow for the DSLR and Go Pro crowd.
unquote
Edit:
In
this test, a more typical Ps CC one, the speed difference is even less than 15% - negligible.