Stack and reach will invariably determine bike fit. And your riding style will combine with your measurements to determine what stack and reach you require. Stem length and angle, steerer spacers, where you prefer to have your saddle, your handlebar choice are all modifiers of the required stack and reach. Study up a bit more and find a shop you have faith in. If you are still concerned, perhaps investing in a professional fitting before and after your purchase would be worthwhile.

Some folks just work off their current bike and the understanding of how it works for them and compares to the new bikes under consideration. Over a period of 32 years and through many bikes, that has always worked for me.