What is the difference between the John Deere 6R 165 and 6M 180?

Here is how the John Deere 6R 165 and John Deere 6M 180 compare on John Deere's published specifications:

• Horsepower: John Deere 6R 165 163 hp vs John Deere 6M 180 178 hp
• Pto horsepower: John Deere 6R 165 129 hp vs John Deere 6M 180 140 hp
• Weight: John Deere 6R 165 17990 lb. vs John Deere 6M 180 19180 lb.
• Fuel capacity: John Deere 6R 165 74 gal. vs John Deere 6M 180 85.9 gal.
• Wheelbase: John Deere 6R 165 108.8 in. vs John Deere 6M 180 110.2 in.