Those fitting "rules" are, at best, rough guidelines, and should never be taken as gosple. Only you know when you are comfortable. I'd try a 100 mm stem first and see if the improvement is enough. If you have (or get) a stem with a removable faceplate, changes are easy and you can try different lengths quickly. If you buy from an LBS they will let you try different lengths right at the shop.

BTW, how is your stem angled? If it's a down angle and reversable, try installing it pointed up as raising the bars may also make you more comfortable.