We clocked OBDLink S at over 120 PID/s with the ECUsim. MX performance varies depending on the Bluetooth modem on the host side, the best dongles we've tested get 60+ PID/s. It sounds like you've got a bottleneck somewhere.
Some software corrections enabled us to start seeing about 80 PID/s with the ECUsim and the MX. 100 PID/s for the S. There may be some area for improvement in the software still.
Former author of LinuxICE, nghost, nobdy.
Current author of Automotive Message Broker (AMB).
Works on Tizen IVI. Does not represent anyone or anything but himself.