final drive + flywheel.. would be my words of advice

and as mentioned earlier, gains are to be had with an ecu, it really doesnt matter if its power fc, pro ecu, hondata, etc... but it would do you the world of good to do some research and speak to people in the know as to what your goals are with your car and the type of ecu which will help you achieve your goals, it will work out cheaper in the end