I'm on my first run. One thing I notice is that my prestige point gain has almost crawled to a complete halt after 20 pp. Very disappointing.
Thanks a lot for your comment!
The PP per Prestige level increases with a logarithmic function. This means that the curve is strictly monotonically increasing, but the gain is getting smaller and smaller. When the PP doesn't increase (noticeably) anymore, it's time for a prestige.
You can get more PP on the next run.
Don't be disappointed, it's bad for karma. :-)