How to speed up Radmin
To speed things up, you can disable the wallpaper on the remote computer.
You can also decrease transferred color depth in Remote Screen – General Options – Color Format menu in certain connection properties. The choice of color depth is much deeper in versions 3.x.
If you are connected via a modem you can't have update rates higher than 10 per second, just because signals can't physically go there and back more than 10 times per second (ping > 100ms).