I think you are concentrating too much on RPM's. (Ruin peoples motors) Ill rather work on the midrange then peak power overall

Going to a bigger displacement (b20) will be the more efficient way of doing things but if you know better with the 1.8 then its your choice

Listen to the guys that have done it already. Dont be stubborn, listen and learn from what have been said on both ozhonda and clubitr