I run a small track where 22mph seems to be the max that even the better drivers can hit. 5400kv falls right in where we can gear it for easy driving, then change to a larger pinion if we want to blast down the street to impress the kids. The 6800 is fun on the street, but way too much for our track.
I actually prefer a larger can motor like a 24mm motor with lower kv. I use a Turnigy 24-35-4400kv in my 18T and it is faster than the Mamba 5400's, but I can control the power.