I bought a Columbia FL with a CAT C-11 and 10 spd ultra shift. I get 10.2 to 10.6 Turning 1100 rpm at 57, 1350 at 68. After putting on ECOFLAPS, I noticed the truck doesn't downshift as often on some of the regular routes. Mountains are never a problem, as is severe cold. With 214,000 miles I have had it in the shop one time for unscheduled maintenance when the wiper motor gave out (my fault). My previous experience was as a driver for an owner with a New HINO. I had to drive it slow to get decent economy (52mph would get 9.5 with a lite load and a tail wind). This caused many too long times behind the wheel on what would normally be easy runs. Mountains were an big NO NO and I swear I heard it cry when I accepted a load to Salt Lake City Utah. It broke down several times and the fuel would gel at anything below 6 degrees F. even with anti-gel. The guy bought three of them, all broke down regulary and although they had a "good" warranty, it always took several days to get approved and fixed...the poor guy ended up bankrupt because of those trucks. So class 8 yes class 7 with the right engine/trans etc. yes but the low horsepower ones of the 200-260 range I would stay clear of unless its a regional truck in flatlands.
GOOD LUCK.