I'm using Mikrotik 5.9 as a PPTP Client to a Linux PPTPd Server.

It connects fine, but it averages about 15Mbps or less.

When I connect to the same server with Windows 7, it averages about 40Mbps

Windows uses MTU=1460(default), and the Mikrotik also has MTU=1460 (default).

The PPTPd server also uses MTU=1460 as default.

Now, if I change the Miktorik MTU to 1300, it goes much faster... but only for awhile. The next day of being connected, it is back down to 15Mbps or less. A quick disconnect and reconnect and it is fast again.

So, the bugs seem to be as follows:

MTU above 1300 (or so) make the connection slow, even though there is definately NO fragmentation.

After awhile, it slows down, even at MTU 1300, and the connection must be reset.

Does anyone else use Miktorik as a PPTP client and able to offer advice?

possible, Mikrotik uses userspace PPTP client & server software.
I have a lot of problems, mainly stability & performance issues on my Q6600 + ROS 5.6, 5.10, 5.11, 5.12 as PPTP bras.
When i use a free Slackware Linux + accel-pptp (0.8.5!) i never seen a 100% LA on 1 of cores of my CPU.
When i bought MTK ROS - troubles began.