If you don't know what youre trying to accomplish, but want to fiddle with you stem / fit regardless, fine.

just do two things:

1) carefully record the current size and position of everything before moving anything.

2) get a cheap 90, 100 and 120 stem. $60 more or less. Now play with them and see the differences they make. Add and remove spacers.

then when you get the fit you want, or when you get fit by an actual fitter, you can get a "nice" stem in the size that your trial and error has indicated.