What is considered a high ping in which it is not possible to race with other people in rFacto2? 200, 300 ms?
Ping from player to server? I'd say max about 250 should be good. You can make the game ignore contact after some ping, I set it to 400ms but never saw this in action despite having a guy from Australia racing with us, he is usually with 350 ping to me (I'm in Brazil) and we race fine in both rF2 and AMS
200-225 ms is okay. 300 ms will exhibit some warping. Good ISPs are sub 110 ms. I consistently get 200-225 ms on a rural cellular connection in USA to servers in England or Australia. The same gear in an urban location resulted in 100-110 ms. Biggest problem, assuming no warping, is that your ability to respond to opponent moves is delayed by 0.1 second compared to most other players, so it's important to consider that in traffic & braking zones.
I typically dont see any warping on our league server until someone is over 250ms. Luckily, for the server we use all drivers stay under 150ms most under 100ms, even the euro drivers.
In our league everything above 200 ms is considered a bad ping and a reason for someone to be kept apart from a race.