I've used 78" on the shower head for years. I've never had a complaint. At 6' 6" off the floor, that's a good measurement. I suppose the additional 2" is a good idea. It would accommodate those people out there who are a little taller. Yeah, I like it.
OK, I'll change it to 80"
As you know, some of these measurements are not code. I've been working on a pile of business-card sized cheat cards so some of those guys out there who don't have as much experience will have something in their wallet for quick reference.
Thanks for pointing out that I failed to mention the 4" above the tub rim and I forgot to mention to build the entire shower assembly out of copper. Pex is cheaper. But when it comes to install, that copper really makes things easy.
What I'm trying to do is get very solid measurements (especially backers) that I can give to the framers. Let the framers put in the backers. Let the framers frame behind the shower the RIGHT way instead of putting a stud dead-center of our valve. We're plumbers. We don't carry framing tools on our truck.
Two things that will make your jobs go much faster. One, let the framer frame to your specs so you don't have to f*ck with backers and you don't have to f*ck with moving studs (and then adding studs when moving a stud causes the framing to deviate from code). Two, have the guy digging the footings to go ahead and use his transit to dig your sewer line (and even a graded trench (based on where you tell him to dig). That way, you'll never have dig gravel or fight with the french drain or knock a hole through the foundation again. It will also save you the cost of a 2nd backhoe trip out there. Since he's digging with a transit, you'll never stand in a ditch with a shovel trying to get grade, and you'll never have a contractor freaking out on you because he wants to landscape or pour the sidewalk. In addition, when it comes time to test your water lines and sewer, all you have to do is turn the water on and fill most of the DWV right at the tub. Also, you use city water to charge the pipes (so instead of pumping air from
0-100lbs for your test, you start the test at around 70-80lbs. Not only does it save you time on pulling hoses and testing, since you are mostly charged with water, it makes it very easy to find a leak. (you ever tried to LISTEN for a leak when you have nailguns and other tradesmen). Do it my way and all you have to do is look for the drip. If you dont' see the drip, come back a little later and look for the puddle.