Hi, can you please run real traffic measurement instead of Mikrotik bandwidth test ?
I don’t think that PPTP, PPPOE or L2TP traffic is slow on Mikrotik routers, if it was slow, I can guarantee that Mikrotik is not used anywhere. But it’s widely used with high speed plans and it’s working.
I think this is the issue of your local configuration or network design, maybe there is a MTU issue somewhere between points, that can cause MSS TCP problems and TCP cannot send large segments of data , maybe there is wrong queues settings, who knows.
Regarding accel-ppp - I asked our engineers to write a description of configuration, hope they will do it during this week