Scant little. I mined data from TB going back to '05, before I made the leap to adapt the B21F to my 940 (nearly complete, but yet in process).
In all those threads, lots of "butt dyno" and "empirically determined" info.
Earlier than that, I believe someone had some EGT data which indicated a lean cylinder.... which was guessed to be caused by an intake constriction. I did find a thread with flowbench data, but there was no "head to head shootout" comparing the B230FT to the others.
I made my decision based upon PM interviews with 3 folks who converted from the B230FT to the B21F; 2 in Europa and 1 in Canada. The only dyno data I've seen for the B21F (E in Canada ?) showed a brilliantly flat torque curve, as opposed to the peaky curves I've seen on several B230FT intake data.
Like you, I would have suspected LATER would be BETTER. The notable differences in design are (1) runner inside diameter and "straightness", and (2) the 2X or 3X increase in the common plenum. Since there is nothing unique about this Swedish 4 banger, intake design theory illuminates the differences those elements make to performance.
Last - my $ is on the B230FT intake for improved emissions and idle quality.... the WHY.