My first 3 months were with the way long 9cm stem and I could not get comfortable with the long reach. Switched to a 5cm stem which felt instantly WAY better and seemed just fine. It certainly solved the problem at the time.

However, after another 5 months of riding on this short stem, I think my core muscles have strengthened and I've become a better and stronger rider. So now I'm starting to bump up against the limitations of the shorter stem whereas before it was simply a matter of being far more comfortable and I wasn't pushing myself or the bike so much.
My next step is to try a compromise- switch to a 7cm stem and perhaps my stronger core muscles now will help me feel ok with the reach increase. I feel almost now like I could USE an extra cm or two in the "cockpit"- odd how our needs might change as we get stronger. It's a subtle thing though, and my bike is still quite comfortable for me as it is now, so I'll swap the stem for a 7 the next time I might bring it in for some work or a tuneup.
Nothing like first hand experience to help one figure all this stuff out!