Can you point me to something that will explain what you mean by "ratio-range matters more than speeds"? I am not sure I follow...
Speeds /Vitesses is just how many Cogs are stacked up on your rear wheel.. a hardware count.
gear ratios is Math .. Numbers.. tooth counts , how many times does your rear wheel turn for every time the crank goes around once .
and that multiplied by how big your wheel is.
like forty two is twice 21, so a 42 chain ring and a 21 rear cog 42:21=2:1 ratio wheel turns twice .. 26" wheel? ...
not good at multiplication or division, with a calculator ?
People wrote programs to do the heavy lifting for you, such as
Sheldon Brown's Bicycle Gear Calculator