Beyond a certain point, other factors come into play more. I mean, have a look at Anthony's
Sydney Harbour Bridge and you'll see that people can go absolutely mad. I can't remember the peak or average r_speeds from that map, but I'm sure they could be hit in completely different ways with rather different hits performance-wise.
Depends on the player's hardware, too, largely. I mean, I've played a map recently that I think reached about four thousand without noticing any framerate impact, but my PC's pretty respectable.