actualy this is very similar problem like in http://forum.mikrotik.com/viewtopic.php?f=2&t=29321
, but thats post is from 2009 and nothing change from that time.
we try large number of combination and optimisation found in this forum and nothing give as satisfactory result
we dont wana throw problem on mikrotik, we just wont some sugestion about possible amount of pppoe session per several x86 server combination.
its very hard, experiment on live subscribers, with hardware cost several thousands dollar.
and please we tested concentrator on up to 700 pppoe connection for several months witout any issue, so dont tell me you have 300 hundred or something connections and everything is ok, question is on whitch modern x86 server based expencive hardware is possible several thousand connections, 1500,2000+ ????