The stem length as it is should be fine for most 6-footers on that 58cm frame, but you need to get a completely comfortable reach to the bars when you are squarely on the saddle. So firstly I would skoot the saddle forward until the reach to the bars is sustainably comfortable while riding in the drops of the handlebars. From there, you will want to test a range of saddle height adjustments.

I see a lot of road bikes these days fitted with the saddle too far back, which rotates the lower body rearward, thus forcing the rider to bend more sharply at the waist. I assure you that road bikes are not best fitted that way, as it makes it impossible to ride in the sporting manner that the bikes were made for.

Moving the saddle forward rotates the lower body forward, which may require a slight tilting down of the saddle to where only the front half of the saddle is level, assuming the saddle top has at least some concave curve to it (kicking slightly up toward the rear).

A more-forward saddle makes for a quicker and lower-effort "heave" up to a standing position, as when attacking rolling terrain, so helps one maintain pace despite changes in grade.

Here is one of the larger bikes that I've set up for myself, and which is comfortable for me to maintain speed on though the hills here while on training rides. It's an old criterium racing bike, with as big of a frame as yours, but I'm only a long-legged 5'9" (175cm) tall and 55 years old.
Again, note that I have a comfortable reach distance from the saddle to the bars, by way of moving the saddle forward.