with new technology you can race a 10.5 or 13.5t nearly as fast as a 5.5t.
Think that if you go for something "hot" like a 4.5t for exemple, you will need a good speedo that can take lower wind, battery packs that can take the extra power without melting, and a chassis that is made for top speed where you will not chew or melt differential gears.
And from what I see (and I do not know that model) this is not a top chassis with his centre shaft.
get a good combo speedo/motor with variable timing in say 10.5t and some good batteries 2s in 60C to get good power, the size of battery (3800/6200) is more for the lengh of time you want to run your car.
then depending on your buying, make sure you run a good ratio not to burn everything.