The 6.0 with 3.42 gears will likely yield better performance. The 4.8L with 4.10 gears will probably be more fuel efficient. I wouldn’t expect a very big swing in fuel economy in going from 3.42 to 4.10 gears. Around town fuel economy might actually improve a little.
When I had my Bronco (351W , 3.55 gears) it got around 11-15 MPG, I put on a small 4 inch lift and fitted 33 inch tires. 4.10 gears would effectively put me back to stock, but I went with 4.56 gears for some added acceleration. I want to say that I ended up with something like 4.00 effective ratio. It ended up being just about right what I wanted. Fuel economy was about 9-13 MPG after all that
Since this is a just for fun exercise, do both! Then as FoDaddy, you can add a lift and tall tires!
I think the 4l60e trans would be…adequate with the 6.0 if I didn’t tow often or heavy (I don’t). It was used behind the 350 and did…ok.
I’ll probably do neither unless something breaks. If the 4.8 poops the bed, a 6.0 is going in it’s place for sure.
I may talk to a guy that does ecm tuning, just for fun. Nothing extreme, but I’d like to see if he could alter the shift points a bit. I’d like for the trans to hold gears a tad longer. Somewhere between how the trans behaves between normal mode and tow/haul mode would probably be ideal and satisfy me. If he turns up the timing a bit and the motor pops…well then, decision made. 6.0 
Plus I’ve always been curious how much difference a performance tuner even makes on a stock engine with no turbo. Only one way to find out.