So, I dropped another 16GB in my machine to bring it to 32GB. Major improvement. A little observation, my machine's general memory usage hovers around 12%-17% (~5.5GB on the high side), that is just O/S, services, and maybe a browser tab or two open. Loading up the Updater + the Star Citizen app and playing brings that memory utilization up to 44%-54% (~17.25GB), I did not see much above 54%.
The game, as it stands now in PTU, seems to wants ~12GB of available RAM, which could spike up depending on how many entities may need to render, etc., before it will require virtual swaps. This VM access seem to be where the lag spikes and CPU spikes are occurring. I only have a 4GB video card, so not sure if & how much RAM may be allocating there. I am thinking if you have an 8GB video card RAM usage may be less.
If you're running 16GB ... an upgrade to 24GB (2x4GB), or 32GB (2x8GB) would give you a much better experience.