[OpenSER-Users] Openser performance with rtpproxy

Hey I've got a simple openser configuration working with rtpproxy. It's mostly copied from http://www.voip-info.org/wiki/view/OpenSER+And+RTPProxy but I don't handle registration and do only nat helping (for current testing I don't even save location - Contact / URI headers are enough). I've tried setting up sipp (no authorization, just invite, send 7 secs rtp, bye) and standard UAS scenario on the other end. I start to get retransmissions / timeouts when I use 2 hosts and ~70 simultaneous connections (total). Typical delay is ~250ms (not network delay - it's on gigabit LAN). I've used the same sipp scenarios for asterisk before and got up to 700 sessions running correctly, so I believe the problem is with openser config here. How can I check what causes the problems exactly? Is there any typical performance problem? I've tried googling already - couldn't find anything obvious. I'm running svn version. Thanks for ideas.