Biggest tooth gap and/or biggest ratio of a single shift.
Total range of derailleur gears has gone bonkers with the current Shimano MTB 33-speeds which have 6.6:1 overall. I think the only things that beat that have a third shifter.
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."