On this PC I can run 24 UF clients. It starts to run poorly so I seldom do it and normally just run 18. I have two clients installed. One that I have minimal graphics which I use as a main. Usually, two toons will be loaded with this client. The rest are running on a client with everything turned off. Stick figures, etc. The worst thing that will happen is the two characters on the minimal graphics will lag behind the other client. Meaning if I check on the stick figures client the mob is dead. But the fight is still going on the minimal client. Bothersome but I would rather deal with that than all stick figures.
On RoF2 this PC cannot even handle 12 clients. Lag is horrible and unplayable. Today getting them to just load was a problem. Once I got to 4 clients running, I would launch a new client and it would crash before it got to character select. Sometimes the client would load sometimes it would crash.
I downloaded another RoF2 client from another source and will try that. Just to test.