It depends on how it is setup, my current design I am playing with will have to have a jackshaft and 2 chains any way.
The trick is to setup a standard 21 speed (easy to keep track of and cheap) and use that for 90% of shifting and have 3 speeds on the other chain to set a range ie low for monster hills and a ludicrous high range which would not be used unless you have an aero shell. the idea being to not normally use the extra gears like a 4 wheel drives high low setting.
Depending upon route I will run into hills that are over 30%, if I have a heavy shell I will need every gear I can get.