As I posted earlier, both produce similar results, with length and angle being key to what happens when you invert, while the effects of moving spacers is obvious.

Here's a nice little length & angle = rise and reach chart that shows it graphically. To see the effects of flipping the stem imagine the mirror image below and double the rise to get the change. Note, the chart is degrees above horizontal, for your purposes, consider it as above/below the roughly 17° angle of a 0/90° stem.

Reach will not be exactly as per the mirror image, but the difference isn't that big except with high angle stems. If you want to get more precise answers there are various stem angle calculators on the net, here's one of them, offered without endorsement.