You must be reading my mind JE. I hypothesized that the cone was heavier in the later model, borne out by the difference in "feel" of the two cones, the way the 414B was prescribed in the 9842 using tuned ports instead of a simple port in the 614, and the parallel evolution of other Altec drivers, including the 855. Following the path from the WE 855A to the Altec 855E sees the driver morph from an ultralight, ultra high quality speaker (WE855A, WE728A), to the slightly lesser Altec direct equivalent (855A, 414A), to a slightly coarser, less efficient alnico model (855C, 414B/C) to a ceramic version (855E, 414E).
I 414A is more efficient but has a rising response. Its extra efficiency seems to be largely expressed from 1,000 to 4,000 hz. I would expect the bass to suffer in comparison to the heavier driver. I would also expect tube amps with low damping factors to get more bass bloom out of this driver.
The later driver was designed when low power was not the norm (as opposed to the 414A, when 10 watts was still a lot). It has twice the power handling and what appears to be a flatter response. The 32343 crossover uses equalization to extend the highs in the 9842. It actually takes a lot of attenuation to bring the upper mids down to the HF level. For those who enjoy flat frequency response, the lower efficiency of the 414B/C is an advantage since we can bring the HF driver down another 3dB. I also suspect that the driver sounds better with the two 6" d x 3" dia ports than the single 7" x 2" of the 614 cabinet. Interestingly, the port area of the 614 port and the combined 9842 ports are the same.
I think if I were using a SET I would prefer the 414A. If I were using something with a bit more meaty and modern sounding I would probably prefer the 414C with an upgraded 32343 crossover, maybe without the zobel, maybe with.