I was thinking about this all day yesterday. Since the tip is basically getting dragged, and the V bit take a very large bite with each depth change, I think moving fast taking shallow passes is the ticket.
A 40% (3mm diam=1.2mm step over) step over on a regular bit is a normal/large step over. So what is the equivalent step down on a Vbit? I would say less than 1.2mm (not doing trig before I finish my coffee). I would do 0.5-1mm at 30-40mm/s as a starting point. Plastic is super picky about its feed rate though.
The hard part is the first pass is basically just dragging the tip through, so maybe the trick is full depth and getting the RPM and feedrate perfect? So easy in wood, so hard in everything else. I did get it in Aluminum and wrote down my setting in here somewhere.