A change in wall thickness is not very effective, in 3/8" OD going up from .080" to .100" only adds 7% to stiffness.
However, increased OD is way, way more important, even another 1/16" is very helpful. Bending resistance varies roughly as the 4th power of the tube OD.
Example: Keeping the .080" wall constant, 7/16" OD is 74% stiffer than 3/8" OD - if you can fit it into the PR relief holes. A single or double taper may give more room.
I would ask Smith, Trend, or Manton what they suggest based on your RPM, 250 & 600 sounds low but they certainly know better than I do.