[starscream]

Yep, the smaller pinion will produce more bottom end but a lower top speed. You'll need to try different gearing to find the sweet spot. You don't want to over heat your motor or esc (I know, because I've done it). A BL motor shouldn't get over 180F
So higher gearing = a hotter running motor = less runtime
Here's some quick info about motors (FYI)
kv = rpm per volt
The 9L has 2731kv so at 14 cells or 16.8 volts your rpm will be 45880
At this max RPM I would suggest around a 22:1 gear ratio or a 15t pinion. I basically came to this conclusion from personal trial and error.
The 8L has a 3072kv so at 12 cells or 14.4 volts your max rpm will be 44236
You can adjust your rpm by adding or removing voltage.
I personally would favor getting the 9L over the 8L because the 9L runs at approx the same rpm at a higher voltage (more efficiency)