To pile on.... yes, 20mm is significant.

Whether a 70mm stem is appropriate really depends on your fit needs. Also depends of the reach of the bar you are using. Needing a stem that short puts one on the tail of the bell curve, but does not mean it is necessarily wrong. But it does warrant making sure you are on the right size frame.

I have atypical fit needs. I run a 70mm stem on my road/gravel bike. Handles fine.