Dave, the RB300 has a tapered arm tube, which should be superior in resonance characteristics to the RB250, which has a straight tube.
With the removal of the spring, and your other mods, you should be better than the RB250, or at least just as good.
You really should get the end-stub modification,if you haven't already, as that is the most effective mod for the Rega arms.
Also, shrink a small piece of heat-shrink tubing onto the finger lift, since this is known to be microphonic on the Rega arms.
Sometimes a small piece of damping material about 1/3 of the way out from the pivot, is useful, as this is the resonant point on the Rega arms.
With the removal of the spring, and your other mods, you should be better than the RB250, or at least just as good.
You really should get the end-stub modification,if you haven't already, as that is the most effective mod for the Rega arms.
Also, shrink a small piece of heat-shrink tubing onto the finger lift, since this is known to be microphonic on the Rega arms.
Sometimes a small piece of damping material about 1/3 of the way out from the pivot, is useful, as this is the resonant point on the Rega arms.