If you want to race and run 4s,5s or 6s, get the tekin and one of there lower kv motors. Otherwise you can't go wrong with the castle. 4s and the 2650 will not give you as much runtime as say a T8 2050 on 4s, which should be enough power on almost any track.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy