I'm 4.11's on 285/ 24.5's. I swapped out the original 3.42's to the 4.11's. Its geared low enough.
If I size up one size in crane- to a 60-70 ton rt, I'm going to go from a 70,000lbs machine to a 90,000lbs machine or so. And then I'll need 4 axle truck and probably stinger and/or 4th axle on my trailer.
I don't have current plans for a larger crane, but I could see it happening. So I keep my eye out and if the right heavier spec truck comes up for sale, then I would be one step ahead of the game.
If you wait to get the heavier truck until you have the heavier crane, then you have to buy both at the same time (I don't have a really tall mattress). Essentially, I'm looking at horses before I trade my cart in.