Read up on optimizing your system for AE and follow these guide lines, Allocate multiples of 4GB of ram to your processes. At the very least keep the allocated ram in multiples of 2GB. If you use MP rendering then make sure that the total number of processors equals the total number of processors. It's easy to end up with 0 processors actually used if you allocate too much ram to a core. If you are using Ray-traced rendering make sure that you have it set up properly and that you have an NVIDIA GPU properly configured and the latest CUDA drivers installed. You may have to check the "use unsupported cards" box in your preferences because Ray-traced rendering using CUDA is no longer being developed by Adobe. If you do not have or have not configured your NVIDIA card correctly then DO NOT install Cuda Drivers.
Last point, be aware that not every project is going to work well with MP because not all plug-ins and codecs are MP aware. Also, don't make your disk cache too big. No sense clogging up your available drive space and you system bandwidth with a lot of redundant or unnecessary read write cycles.
I really appreciate you taking the time to write this, but I don't entirely understand some of what you said.
Where do I allocate RAM other than in Multiprocessing Preferences? So, if I'm not using MP what program options do I have and where are they?
I don't use plug-ins often but is there any indicator which ones and codecs don't do well with MP?
Can you suggest a good Max Disk Cache Size? I have a 550GB SSD.
I suppose I should also say, I can't find it anywhere on the Adobe site where I can "read up on optimizing my system for AE"!