Ahoi,
recently I upgraded CPU (from Ryzen 5 1600 to 5600x) and RAM (from 16 GB DDR4 2400 to 32 GB DDR4 3200) - and necessarily the motherboard BTW. The GPU (AMD RX 5700 with 8 GB) didn’t change, and I left the graphics settings as they were.
All my former problems seem to be gone! The sim runs smoothly even in complex areas (eg. London), and those occasional breaks (up to one minute or so) are history or very short. I can even use my Oculus Quest in the London area, that was almost impossible before due to bad FPS.
It’s hard to tell what exactly made the change. I feel that the bigger RAM helps the most. GPU and system RAM had often been at maximum before, possibly the machine then had swapped to SSD (which might have been responsible for the breaks).
Now eg. in London area the GPU uses all its RAM and about 1 to 2 GB of system RAM. But since 32 GB seems plenty enough there is no problem with that (in this case about 20 to 21 GB of system RAM are in use).
So, if you have similar problems and a comparable scenario, perhaps give it a try?
BTW now the GPU is the ‘show stopper’ (at a high level). Perhaps I’m going to fix this in the future when the prices are hopefully back to normal 
