The ISL IS common in 40 plus A's. 400HP and 1200 Torque has a nice combo for hills and MPG. The ISB motor while will get you there is the baby of the bunch ISB ISC ISL ISX, the bigger the coach the bigger the motor and you will be in the 3000 trans 6 speed needed for the power and weight.The pushers are some quieter but the ride is floating not bumping down the road. One great advantage to me in the pusher is also most have upgraded most everything, but the top end gasser's have been catching up. If you stay in the 36' range the small motor is in more of the coach's but there are lots with the ISC and the ISL.
LEN