The best method is to go out and buy 4 different stems and try them. Honesty.
Bike fits are a scam. Trial and error for your own body and own needs only way to figure this out.
You also need to consider changing your bar width if you alter your stem length/height more than 20cm.
For starters, flip your step up, if it's down. Also, is your bike the correct size frame, and/or is it a racing frame or an endurance frame? Trying to make an aggresive racing frame into a casual endurance bike is not really going to work great.