it is not a case of not trying things out, it is a case of a very well tried and proven thing over and over again, small combustion chambers do not give high speed power,
that is fact proven by major race teams and major engine tuners. and dont forget a race team dont even care what happens to the motor as long as it wins and last
till end of race.

smaller chambers Will give more low speed power/torque call it what you like. would be good for say water ski-ing or wake boarding as the speed is slow.

your small chamber head is not what has given you more rpm, that was the raised exhaust porting and the no limiter electrics..

shame about the tacho, what make is that one ?