Brushless Emaxx set up

hi all,

I have my e-maxx running on the Novak HV set up for a while and would like to go one step further...

I currently have a BK 9918 Bruhsless ESC, and a BK 20S (16XX RPM/V) motor in my hand, i used to run 2 pack of 7.2V NiMh in parallel.....since i also play boats, so i have a few packs of 9.6V NiMH. I planned to hook up the system with 2 pack of 9.6V in parallel (= 19.6V).....

Just wondering what kinda gear ratio should i be running for a more efficient setup (normal run time, acceptable top speed)
What size of pinon & Spur gear should i go for to obtain that?


Thank you in advance for your suggestion.

BR
Tom