To see the true speed of arpReach, switch the system into "test mode" (by going to Setup / System Settings / Outgoing email and checking the Enable test mode option) and "send" a broadcast. This shows the speed that the software is running at when there is no overhead of waiting for the server to send the email out.

Our own tests show a speed of 300,000 to 400,000 emails per hour on a Liquid Web dedicated server.

Any slowdown out of the "test mode" is down to the sending limit and other resources available to your account by your web host.