If you want a wide spread gearing try a 130/74 BCD 5 hole triple crank-set like a FSA Gossamer, cut down to 155 mm by Bikesmith, and use a 53 Q ring (55.5 t max, 50.5 T min), 39T Q ring (41.0 T max, 37.0 T min), and a 24 T circular low range chainring, and a convential 11 to 32 10 speed cassette.
On my Silvio V1.0 with 700*28c tyres (2.093 m circ) that gives me a 20" to 132" effective wheel diameters, or 1.6 M to 10.6 M moved per crank revolution, 673% variation.
At 120 cadence in high gear, I am doing 76 kph, ONLY when going DOWN a hill!!!!
If you went to a 406 (20") 50 mm big Apple, (1.555 m circ) with 24 T, 39T Q ring, 53 T Q Ring, and a 9 speed 11 to 34t cassette.
then 14" to 101" effective wheel diameters, or 1.13 M to 8.07 M moved per crank revolution, 536% variation.
At 120 cadence in high gear, you would be doing 56 kph.