I have ridden everything from 90 to 130mm and it made zero difference to handling but a big difference to fit. Those that say you are shortening the lever arm must ride their bikes funny, last i looked the handlebar is the lever that your arms push and pull. At the small (few degree) movements while cycling at speed the stem length is insignificant as a lever in steering. No one would blink if you changed bar widths by 20mm. Of course some people will fit a short stem and feel twitchy and conclude that short stems are twitchy - all they have proven is that the wrong length stem for them felt twitchy

You have said it is not possible to position your saddle where you want therefore you are changing the stem to compensate. The stem length is independant of saddle position and cannot compensate for a incorrectly positioned saddle. Sounds like you may be making a poor adjustment to compensate for another poor adjustment. Think carefully