very interesting project you have going. i will be following this closely
i also happen to have some realtracks and my mini-z seems to do ok on the very small portion i have laid on on the floor. i ran a stock dnano on this same small portion which also did ok. i agree that anything with some high speed will require more grip from either tires and or track.
what tires were you using for these test? testing tire combinations is going to be much cheaper and easier than modifying the track surface.