I use eth6 as a pppoe server for almost one hundred customers and some of them ( always the same 
) have problem to download and surfing is slow .
Is there a problem or have i too many customers on the same interface ? 
wich routerboard do you use?
do you have only a pppoe server in routerboard or also mangle, queues, etc?
I have almost 500 on an RB1200
Over 1000 on a VMware machine (running Routeros)
no issue
I have a RB1100.
I use mangle rules and queue tree ( cpu load 19% max )
I also use nat to redirect customers to my squidbox
If he has 500 on RB1200, then you can probably have 1000
Ok so the problem seems to come from my switch ( linksys )
i’ll try to fix qos on the switch . ( wait and see 
)