As my name indicates, I'm a little new at Gleaner combine ownership, so I don't profess to hold a degree in Gleanerology like Tbran or Tom langan. My understanding is that the R52 has more horsepower, bin extensions, a heavier planetary drive system, and a chromed concave cage, all of which the R42 DOESN'T have. I opted for the R42 because I felt that it best suited my needs. The chromed cage is nice if you're combining a lot of beans; - it wears better I'm told. And the extra horsepower and heavier drive train is nice in muddy or tough conditions, which I seldom experience. Bin extensions are nice..., what more can I say. I tried both machines and chose the R42. One thing I do know is that the R42 WIll NOT keep up to a Deere 9400_9410 in wheat; - corn and beans maybe, but not in any crop with heavy straw!