A second reg (quality brand) with HPA will do nothing but help. With Co2, I would say its almost a must to be consistent unless you live some where that is always the same temp.
Matching or under-boring will help, period. Plus it will stop roll outs.
A regulator of some kind, spring kit & barrel set or insert set is what you will need to see a very consistent marker. Ive spent a good bit of time tuning mine & it is on par with the Intimidators I used to run, +/- less than 3fps through out the day.