Something 1/5 scale I would not have the room to run, thats why I'll stay with 1/8, and no bigger.

I hear novarossi, rossi, tops motors are extremely good. I have no experience with them though. The serious racers at my track run these, the OS engines are very popular. I own 2 os .18 motors and i love the power and tunability. You don't need to be an expert tuner