Not sure about soybeans in particular, but generally I have had good results with any hi-inertia cylinders I have installed. As I said in the walker maintenance thread, there is a gain in capacity simply due to the cylinder maintaining its threshing speed. Dust vibrations are also a thing of the past because the cylinder is sealed. (No more dust on the back of the rasp bars) This also is easier on the variable drive belt because it does not get the shock load of sudden cylinder speed changes. The only drawbacks would be initial product cost, installation time/cost, and you can't inspect your concave and beater by looking through the cylinder anymore.
jkane, remove your filler plates. You won't need a very expensive cylinder change. Added what feels like 50 hp to my 9500 in very green stemmed beans. Runs very smooth, and no dust can build up in cyl. anymore. Leave them out for corn, too.