Best advice I can provide is to get on any bicycle with gears on the rear
wheel (Cassette) and gears on the pedal crank shaft (chain rings)
That is the same setup most any vehicle has, except for 4x4's which has another
set of gears in that mix
The new automatics is like having more gears on the chain rings than before
Old 3/4 speed vs today's 6-7-8 or more speeds
The rear Cassette will make no matter how many gears, as our TV's has mostly
one (some can have two) and this is where the choice of gear used will tell
On the flats, just about any gear will do, but the higher gear (smaller numeric)
will take a bit more to get it going, but will allow higher speeds with
less pedaling
The lower gear (larger numeric) will take less to get it going, but will
top out in lower speeds because you can not pedal that fast
No difference, other than your legs vs an in-animate (ICE, internal combustion engine)
has limits on how fast any one architecture can go
To bad not enough folks actually cycle out there...