Why try on a stock cylinder, you can build your own ports but there is no replacement for displacement...I didnt make that up.
The way I see it is, I get paid pretty decent, lets say at least 20 dollars and hour for ease of math. Now if it took me 40 hours to make a really fast stock cylinder, wouldnt I be better off working for 50 hours and going out and buying the performance cases, kit, ect. I'm not a full time tuner. I'll do some modding work but I wouldnt waste my time trying to get a stock bore to outperform a kitted bike, I'd rather waste my time working and getting paid. To each their own...but dont assume several hours of work on a stock cylinder will make you just as fast as a ported cylinder kit.