When ridden in the same manner, the bigger engine is always going to have worse fuel mileage (all other things equal). However with the big bikes you don't have to twist the throttle as far as on the small bikes to do the same work so thats why some riders are able to get better mileage out of a bigger bike.
Another thing is in street riding there is alot of constant throttle operation as well as smoother throttle openings (in my experience). 75 miles out of 2.1 gallons is 35.17 mpg which isn't too far of what your 450 exc-r gets. Plus your KTM has that 6th cog for more relaxed cruising:thumbsup:
How do you like big orange?
6th gear cruising is freezing and fast. i'm going to gear it down, but its a nice cushy ride that does great offroad. so i'm more than glad