I have a bicycle with the Sturmey 5 speed hub. I hardly use it since I'm in love with the Nexus 3 speed. However, these are some of my observations.

1. Learn how to put on the rear wheel -- I know this sounds strange for for some reason, a flat forced me to the LBS because there is a method to putting on the rear wheel for this hub! I never had trouble with 3 or 7 speed but the Sturmey 5 requires a certain procedure or the hub will keep slipping!

2. Find out what gear your most comfortable riding with a load --- I've never rode the bike loaded but whatever gear you do find it easy to ride loaded is important. I ride the bike 95% of the time in 3rd gear at 54 inches. This gives me two high and two low gears. Since you are touring, maybe a low fourth gear that you can ride in all the time might be better. This will give you 3 low gears and one high.

3. You won't save much weight from the Nexus 8 --- The Sturmey 5 speed looks about as big as the Nexus 8 and probably close in weight. I guess this is the main reason you'll find most hub geared bikes in either 3, 7 or 8 speed.