I just found this fitting guide:
The Science of Bike Fitting | CyclingTips

I was VERY septic. I already did the fitting for the saddle height and position (145-155 knee angle + pedal axle in front of the knee). I checked and surprisingly, the guide got it right for the saddle position & height. Since I never played with the handlebar positioning, this trick is of great use as I don't need to do any measurement. I actually have ~95 mm stem. With the hand "trick" I should have something closer to 130 mm.
I have neck pain when riding after ~ 2 hrs. My neck is like always compressed and I would like to try a new set-up. I live in Canada and MEC is a great seller of outdoor stuff. They have some adjustable stem but none them are 130 mm (nor do they have in stock 130 mm stems). The longer adjustable one they have is 110 mm and bad looking as shizzle.

First, I wonder how true is this measurement. Secondly, my stem height is far from respecting the 3 fingers "rule"... it is more like 6-7 fingers. Got narrow fingers but even with larger ones it would still requires 5. There's like 3 rings that I suppose rise the stem. How easy is it to reduce the height?

Would you get right away a 130mm stem? The most popular seem like 6 degrees.