Shifting is a very powerful tool that is up to driver preference. Personally, I don't run a shifter unless my specific strategy requires a really low gear (~4 ft/s), or a really high gear (~19+ ft/s). A single speed 3-CIM gearbox at ~16 ft/s is my favorite setup to run because most of the time I really don't need shifting, and the extra acceleration and power from the extra motors makes the single speed just as powerful, and mathematically you gain the biggest benefit from the extra motors at that speed.

Just my $0.02.