Between the Raritan, Vetra and KVM-based converters, I personally found the Raritan to perform the worst. I wonder if the types of PS/2 mice tested has something to do with it. My test mouse was a Logitech MouseMan (trackball). My screen resolution was 1280x1024 in Windows NT 4.0. I do recall reducing the resolution, but still found some lag and jumpiness, which decreased with decreasing resolution. I am accustomed to using a PS/2 mouse over a serial mouse, so my judgement might be somewhat spoiled in this regard.
dirkmirk, would you be willing to test your Raritan on a system which has both a PS/2 mouse input and a serial input using a screen resolution of 1280x1024? Test the mouse on the PS/2 port then compare it directly on the serial port. For me, even at 1024x768, the mouse had so much lag I found it difficult to navigate through the Start Menu programs. I do recall adjusting the baud rate and other various settings but to no avail.
Plan your life wisely, you'll be dead before you know it.