ok, so if i read this correctly, then the p2pool folks say: if you have 10 MBit/s or more use 32 in-peers (that's 40KB/s per in-peer).
Don't use more than 1000 because of the linux file limit (which can be changed)
So according to their numbers, with my 20 MBit/s limit i set i should choose about 64 in-peers.
I just looked at the upload-traffic of the last 21 hours.
In total i used 44.55 GB of upload-bandwidth in that time, which is about 4.71 MBit/s or 603 KB/s.
There were about 130-140 connected peers in that time.
That equals about 0.03492 MBit/s or 4.47 KB/s per connected in-peer
With my 20 MBit/s limit that should allow for ~573 peers. This is average speed though, and there are probably spikes in network usage all the time. So if i apply a buffer of ~50% i should be able to serve about 256 in-peers with an average of 10 KB/s per in-peer.
I'll set it to 64 out and 256 in and let it run a couple of days and see how it goes :)
There have not yet been more than 150 connected peers anyway