I personally do a 7x7x5 reactor with resonant ender on the sides and diamond blocks or cryotheum between the rods, which are in a x formation, except no rods in the corners. Produces 20 thousand RF/t by itself, depending on your config setting. However, I strongly suggest experimenting in a test world as you could figure out a better design. Also, use turbines from Big Reactors, as each turbine can produce 50% more power then the reactor can itself, and a well designed reactor can sustain multiple turbines.