I would agree with Mike. The 6.0L is a good engine, and stock they will work very hard and pull well. I was at the Fuel Pump and the guy that was across from me and I were talking, He has a 7.3 SD and I have the 6.0 Ex. I asked if he was running stock or had it turned up.... he said he had it turned up, and that he drove it on the "tow" setting all the time bacause it got better mileage.... he thought the "tow" setting bumped it up 30 or 40 hp and "Extreme" was 90 or 100hp..... so..... if he was happy with the performance on tow and it was lets call it in the middle, 35 hp, I believe the stock 7.3 was somewhere around 235hp, so that put him at 270hp.... a stock 6.0, at least my 03 model year is 325hp stock....... so at that point you are already 55hp above a "turned up" 7.3. I love my 6.0 and would buy another vehicle with the 6.0.
Also, argve on this board loves to turn up the power on his trucks..... he had an IDI (the Enterprise) and a 95 Dodge that was up around 500hp. He has driven my truck and said he sees no reason to turn it up...... so someone who thinks more is better, thinks the 6.0 is already pretty much there.....
So I would say, look at the truck you want, and what you want to spend.... an OBS, a 7.3 or 6.0 PSD SD would all allow for a reliable truck and in the pricerange you are looking for. The SD's have more "creature comforts" and the cab is bigger and has more room in it, and the SD's have 4 wheel Disk Brakes... the OBS does not.... these are all something to consider......