Piston life would defintely be a concern since they are not oil cooled, not to mention the difference in compression ratio. I've seen factory stock 7610s crack pistons, not turned up, just worked hard all its life.
Clutch is lighter on the 6610 (12" vs 13"), and the finals are as well (2 speed vs single speed PTO). On the older 7000s and 7600s, the transmission gears and bearings were different as well.
If it was set to 85, I would agree, it would likely be fine, cooling aside.