Interchangeabe tonearms with RB300

Looking to upgrade an arm but prefer not to replace the arm board. My RB300 connects to the arm board using a 1 3/4" (approx) threaded connection and a nut that tightens from the bottom. Are there any other arms that would be an upgrade that use this same configuration?
The VPI arm screws into the top plate with wood screws...not hard at all. It's not a "drop in", but is very easy to attach.
I second Kbell's recommendation of Origin Live tonearms. They have a nice product selection from very reasonable to very expensive and are not only terrific sounding but a great value. I believe Jay at Audiorevelation carries the line.