What kind of comp? What kind of settings? Did you by any chance install the cuda driver? If you see cud a in your system resources then get rid of it.
I have the new mac pro with this configuration:
3 GHz 8-Core Intel Xeon E5
64 GB 1867 MHz DDR3 ECC
AMD FirePro D700 6144 MB
I have no NVIDA graphic card, so Cuda is something I can not use. But is really frustrating. I have to wait 25 minutes for rendering a one minute video with a few effects on it.
Is your comp set to use the obsolete ray-traced 3d renderer? If so, that would make it go very slowly indeed.
Also, what exact version number of After Effects are you using? 126.96.36.199? 12.0.0?
What happens if you do NOT use hyperthreading, and limit your use to the 8 physical cores?