The Kwiggle's 6-speed gearing
The Kwiggle's 6-speed gearing is made for the mountains.
You can ride up to 14% slope with it. So you can get up almost every alpine pass with it.
Limits also exist here when it gets particularly steep.
The bottom bracket gear, like all hub gears of bicycles, is equipped with a planetary gear, which causes an energy loss of about 5-10%..
That's why you're a little slower with the 6-speed than with the 3-speed.