I've got a few hours (less than 50) in a 301 Air Tractor with a Garrett turbine conversion that I flew for a couple of weeks one season. Turbines are nice, reliable, and very productive IF you have the work to afford them, and they are definitely quieter. But, there's just nothing that compares to the sound of a thunderin' 1340 powered Cat or Air Tractor coming over the tree tops just a little after daybreak on a still, hazy spring morning. You can tell that sound before it ever gets in sight. I used to love that first flight of the morning.