Trying to get AE to be as fast as possible, disregarding everything else.
So, I tested render time on 5.5 with and without multiprocessing and with seems to take ~20% longer...
Are my other settings correct here?
Just curious, in what cases multiprocessing is benefitial?
I think I'm on a Nehalem (whatever was before Sandy) architecture, is it different for newer CPUs?
What exactly are you rendering? That is all it come down to. If footage is involved, the file I/O will contribute considerably. Likewise, if you have a single memory hungry effect, it could slow down things massively. I'm afraid it's not as aeasy as flipping a switch. There's an article on this stuff in the help or Kopriva's blog somewhere, but the long and short of it is that different projects will require different settings and only your experience will tell you which works best on your system.
Mylenium's right: there isn't any one-size-fits-all Best Settings For Speed.
I can tell you that you're shooting yourself in the foot by using all your procesors for AE. What's the operating system going to use?