HnS,
Another point of reference... I'm 5'11" and my bench work surface is 34"h. I never use a stool. The top of my vise jaws are 9" above the work surface, or 43"h. I can comfortably work at my vise and drill, grind, cut, file, bend, or weld. Another point, I have a 1" thick rubber mat in front of my bench... that makes me 6' tall.
When I built my bench I played with it a lot. I jacked it up in 1" increments and then put various objects (lawn mower, carburetor, alternator, tricycle, wagon, beer, etc.) on the work surface. I then did a few operations on each object (i.e. loosen/tighten bolt, screw/unscrew a screw, drive a pin out and in. All this to test the suitability of the finish height. In the end, I left the work surface at 34". For me it was a good compromise height. And, I could always slip a 1" x or 2" x board under the legs if I needed it for a special project. So far, I haven't needed to do this in the 22 years since I built it.
Yet another point of reference... I have a second bench I built just for mounted power tools. I have a smallish bench drill press, a bench arbor press, and two bench grinders mounted on this bench. I have a peg board above this bench where I hang my angle grinders, corded drills, cordless drills, cordless impact driver, soldering gun, glue gun, heat gun, equipment toolage, grinding wheels, wire wheels, sanding disks, cut off disks, etc. This particular bench is 8' long, 42" tall, and only 18" deep. This bench is tall so I can stand up straight and can see what I'm doing with the bench mounted power equipment. It may sound crazy, but it works very well for me. The smaller hand-held power tools typically get used on my regular work bench, or on the garage floor, or out in the driveway. I also have some folding saw horses and a half sheet of 3/4 plywood that I can use as a temporary fab table in the garage or driveway.
So, plan your bench(s) well and think about work flow and the tasks you're likely to be doing in your garage. And, don't forget about electrical outlets, power strips, and task lighting.