What is the difference between the John Deere 6M 165 and 6R 165?

Here is how the John Deere 6M 165 and John Deere 6R 165 compare on John Deere's published specifications:

• Horsepower: John Deere 6M 165 163 hp vs John Deere 6R 165 163 hp
• Pto horsepower: John Deere 6M 165 125 hp vs John Deere 6R 165 129 hp
• Weight: John Deere 6M 165 17637 lb. vs John Deere 6R 165 17990 lb.
• Fuel capacity: John Deere 6M 165 75.3 gal. vs John Deere 6R 165 74 gal.
• Wheelbase: John Deere 6M 165 108.8 in. vs John Deere 6R 165 108.8 in.