Hi,
I like to keep gearing the same as nitro buggy. So, I'm using 13/46 with a feigao 9XL 5S lipo BK12020 esc. My buggy is old style & heavy (around 4.1kg

). I run in he tropics so it's about the worst condition possible. Ambient temperature typically around 33 to 34 deg C & humidity close to 100%.
Good for close to 37mph or 60km/h. Plenty fast for racing already. Battery lasts around 15 to 20 minutes.
This setup is stable in the above mentioned environmental condition. I've been running this every weekend for the past 1year+. I did manage to fry my 2S portion of the battery last weekend though but this is due to user error. I did not charge the it fully while I charged the 3S part fully.
Hope this is useful.
Regards,
Joe Ling