I just put a Stewart steel Accelerator on my 2166 this past year. It made a new combine out of it in green stemmed soybeans. No more hammering just a smooth feed. I had read about the possibility of plugging more because it feeds in easier but then may plug quicker. I had no problems plugging and ran about 400 acres of green stemmed beans through. I saw no real negitives in corn. The rotor is a specialty rotor with Gorden rasp bars.
My transition cone was showing some wear and was not the heavy duty version so we changed the transition cone and vanes to the heavy ones. What I meant by no real negatives in corn was that to me it was not noticably better but not worse. It was about the same as the elephant ears in corn. The most difference is in tough conditions. Sorry for the wordy answer to say it was about the same in corn.
We've been running a Stewart Steel Exceller kit for 3 years now on a 2388 with rice rotor (spikes). Made new machine out of it, no more rumbling, eats green stemmed rice and soybeans like nobody's business. Very much worth it!