You will have to modify the rear crossmember too so you should factor that into it. I guess since it is flat in Florida you can get by with 37" and 4.11. The whole point of gear reduction is to go slow. Anyone would spend $475 for 2.42 more in gear reductions. Which is what you are getting with the 4.7 toybox. I can run the numbers later but another option is to put in a 5 speed with the lower first gear and change the gears to 4.88. This will give you 2.05 more in gear reduction and you will have a 5th gear for on the highway. I would go with the 4.7 and be done with it. I had to make the exact decision and ended up with the 4.7 and am very happy so far.
The h55f with 4.88s would give you the same RPMs at highway speed as the h42 with 4.11s but the crawl ratio would only be 54:1. (with no toybox). If you want to use the toybox with the h55, then you have to use the 4.7 gears. I guess you could use an NV4500, but that produces another set of problems.