The big difference for me is the 850 runs more consistent than the 800 day in and day out. I think the better engine mounting, heavier more torque crank, and better electronics make the 850 shine. The 800ho will run good IF your motor mounts, clutch bushings, springs, etc. are replaced every couple hundred miles, and then you have to keep pipe heat hot enough to continually pull peak rpm. Just seems like the 800 is a much more finicky motor and hard to keep up on the wear items. My 850 pulls consistent rpm all day every day no matter what. At 600 miles my clutch bushings and rollers still look great. the 800ho seamed to eat those parts about every 4-500 miles. Not saying the 800 is a bad sled at all, my 17 800 with 1900 miles is still impressive and will put a smile on anybody's face, but the 850 IMO, is significantly better day to day. is it 4-5k better?? only you can decide that I guess, but I know im not disappointed in my purchase