Iv done the same project mate. As above GRPs are very good, Jacos are good aswell but have less grip. I seem to get higher speeds if I run GRPs on the rear and Jacos on the front.
Upgrade your drive shafts to the slash HD ones, there plastic but I'm yet to break one.
Make sure you have a big enough area to us it, iv rebuilt mine twice now after fairly bad crashes, you run out of room very fast lol
I didn't go with the castle combo in the end, I'm using trackstar 2650kv motor and trackstar 150a esc from hobby king. Runs great and have had it at almost 90mph on 4s.
Will be going for leopard motor next and running it on 6s hopefully break the 100mph target I'm looking for.
People say run a gyro but I used mine once and didn't like it. May have set it up wrong but once you get used to it, you won't need one.
Other than that good luck and if you need any help look on YouTube for giostealthr1 or draven3907. Both helped me out a lot when I was doing my project