Guess Apple didn't solve the thermal issues after all
Well... Apple uses cheap thermal paste in the Mac Pro 6,1
Its the same cheap junk Dell uses that dries up and is only rated to maintain 50% effectiveness after 3 years.
Also, it seems some Mac Pro's get "too much" thermal paste when they are assembled in Texas.
This is why most "Mac Repair" shops replace the dried up thermal compound w/ Arctic Silver to "fix" a lot of slow mac problems.
Basically you have bad combo here:
Lower then effective fan speeds to promote the device as "quiet".
Cheap thermal paste that dries up and causes CPU temps to rise over time, compounded by the slow fans.
(There's also issue with beading, but I won't go into that here)
I've personally seen a minimum of 4C reduction in temps for Mac Pro 6,1 by replacing the CPU thermal paste. Use of SMCfanControl will also easily drop 10C in temp from a Mac Pro 6,1.
It truly amazes me that Apple uses the same "planned for obsolesce" technique Dell does.
I suspect it may just be an oversight on Apple's part. (and perhaps a source of the frustration w/ assembly in Texas, but the Foxcon folks do the same thing with the iMac... soooo, who knows)
My 12-core D700 1TB Mac Pro idles at 22C and rarely goes past 30C under sustained loads.
But, I built a wind tunnel shelf, in addition to steps mentioned above.
My Mac Pro setup is ranked #1 for single-core & #3 for multi-core performance for 12-core Mac Pro 6,1.
See my Geekbench scores:
Online Benchmark Results (user dread64)