The R50 will have more capacity and if you have side slopes or hills you will really like the R50. Just keep the Deutz engine clean and have a good air fan on it.
R50 is from 15 to 30 % increase depending on paticular crop and conditions. A definite improvement in grain loss, rotary vs conventional. Also improved ground speed as well as bushels per hour. If its affordable , I say go for it. I've ran both machines, it's a definite upgrade, I don't think you'll regret it.
The N5 had a 50% capacity increase over the l series as did the R5, but the R50 as per Deutz Allis specs. was down sized some. That may be the way that Deutz figured it from AC. The big thing to be very careful on, is to keep the Deutz engine almost "clean enough to eat off of". The cooling fins are more particular than the radiator and the cooling fan blades wear with age and need replacement with age. I do periodic cleaning of the radiator on my N6 and the neighbor with the R60 has to do atleast a daily blow out and normally twice daily in soybeans. The Deutz engine doesn't sell well in this neighborhood on combines due to cleaning and overheating problems. And if the Deutz engine needs "major" repairs, replacing it is cheaper than the parts to fix it. One part that I know of costs as much as a "New" engine or a Cummins repower in the N_R series AC combines.