The 110/125's can hold their own especially with the hi/lo sub-transmission. I've climbed some impressive hills on my '85 125m in low range. The one thing you have to watch out for on the 125's is the shift drum stopper will break and it will miss shift, not engage certain gears or fall out of gear.
1985 ATC125M: Parts
1985 ATC200S: 84 200S Bottem end, 200x Head, 200x Carb, S&S Cycle Exhaust, Wiseco 10.25:1 Piston, Reground Cam with About 1mm more lift(unknown specs).
1988 TRX250X
1983 ATC200E: Total Pile.
"Bout Tree Fiddy" Master of Thy 22RE