I re-read your '15 thread and figured adding my .02 couldn't hurt, so here goes... hopefully it will make up for my unhelpful post in the other thread...
Assuming the '17 SR is similar suspension-wise to the '16, the most you can realistically expect to lower the rear end of that bike
easily (i.e., by shortening the shock) and
without affecting rear suspension action excessively is about 2" or so. This will lower the seat height about 1.6" max, unless you lower the front end too. I assume you've test-ridden a '15 or '16 SR? If not - or you want to go again - you can bring a couple of short pieces of 2x4 (@ 1.5" thick) with you to put under your feet, to get an idea of how much lowering is needed.
When you get your new bike, ask the dealer to adjust the shock preload adjusters completely up, as far from the swingarm as possible (this is
not the same thing as minimum preload) and also raise the fork tubes in the triple clamps about 1/2" or so (you can raise it more later if it handles OK). These two simple adjustments - which were mentioned in the earlier thread - may lower your seat just enough if you're lucky, or if not, at least enough for now. I'd also really check out the suspension on rough/uneven surfaces and see if it's set up right for you, which may need fixing too (might as well do it all at once, no?). Zero tends to set their bikes up very stiff which didn't work for me, and also maximizes that tippy-toe feeling.
If you decide you need work done, there's a shop in Allentown I saw recommended on a Yamaha R6 forum that does racing suspension work and also provides trackside support on race days (i.e., delivery) -
Metric Devil Moto (E-mail mike@metricdevilmoto.com, (610) 833-8271). Tell them you've got a super-fast electric bike with a 40mm-piston Showa that needs lowering; you may get a call-back just from curiosity. Being a race-oriented shop they obviously deal with much more involved suspension work (which IMO makes them an excellent choice), but even if they can't help you themselves for whatever reason, they may well know someone who can - provided they're still in business, of course.
Ray