I made an opportunity to test two coaches with the varying power trains, and I'll share the result in case this interests someone else shopping in the future. Coaches were identical models, but differing trim level; one with 340/2500 powertrain and the other with 360/3000. Same gear ratio in the axle and similar weights, the higher optioned coach with the 360 probably about a thousand pounds heavier due to options.
The 360 powered coach was noticeably more responsive at low speeds and accelerated more quickly from a dead stop. As expected due to torque limiting in lower gears with the Allison 2500. This was a difference you could feel in the seat of your pants.
The 2500 does indeed shift more smoothly than the 3000. Shifts from the bigger transmission were smooth, but perceptible. The 2500 shifts so smoothly (again with torque management) that they were imperceptible.
On a grade -using a short hill that's about 4% at it's worst slope as a benchmark- I ran the hill at 65 with each coach in economy mode, cruise control on. The 340/2500 lost 2 mph on the hill and regained speed after cresting the hill, no gear changes of course. The 360/3000 coach lost 1 mph and then accelerated back up to 65 on the climb, all in 6th gear. Speeds measured with a GPS.
Repeating the hill in normal mode and driving with my foot the less powerful coach dropped into 5th to hold speed.
In the intermediate gears 3-5 (where the Allison 2500 is not torque limited), the difference in these coaches is not really perceptible. Accelerating or holding speeds on a grade in those gears the coaches feel very similar and the performance difference between 340 hp and 360 will not be felt. In gears 1,2 and 6 the effect of having the full 800 lb-ft of torque is perceptible.
