Earlier this year the company I rented my server from switched to new servers. This was the time when driving on fast bikes (for example in mods) went from stuttery performance to almost smooth sailing. As others here have showed it isn't the size of the RAM, neither on server nor (in our case) on the client.
My theory of it is that:
1) I know from Fataal that the game operates on an internal clock of 20 updates per second and that it isn't good for the game if it can not provide at least those 20 updates per second.
2) Obviously it isn't world data that is streamed to the clients (as that is local already) and if everyone is driving it also isn't changes to the world. But it is highly likely that the update cycle is synchronized by the server and that it therefore is not good if the server gets below 20 updates per second
3) In the logfile of the server there is a regular log entry that has information about memory usage AND a number called FPS which is probably the servers updates per second. On my old server this was just above 20 when nothing serious happened and often went below 20, on blood moon for example. On my new server it was above 30 and never really went below ~28 even on blood moons.
Now this is just a theory. But check those lines on your server. If it often dips below 20 FPS, in one way or another your system may not be fast enough as a server.
I don't remember if the old server had hard disks or SSDs for storage, LW will, in his "polite" way, correct me that that can't be a factor, but that could have been another difference between old and new server. But I'm pretty sure you have everything on SSD on your refurbished system so it can't be a factor in your case anyway, right?