If I may "chime in", Rick. Kind of surprised you are experiencing slow downs, as I believe your machine has 512 gig of flash storage, along with plenty of memory. I guess a couple of things to look for/mention:
1. Have you done any "extensive" disk cleanup/maintenance/repairs, from a software perspective? You actually can do a good amount of disk cleanup on your own, and there are some excellent programs available (both free and commercial) that can help you out. Two that I use (and have been using for along time) are Onyx, and Tech Tool Pro. I recommend both of them very highly.
2. How much free space is on your internal SSD?
Now, as far as High Sierra is concerned, I have two Macs: a late 2012 Mac Mini with a 256 gig SSD and 8 gig of memory, and a mid 2017 13" MacBook Air, with a 252 gig SSD and 8 gig of memory. I make a concerted effort to keep my Macs "lean, mean, and clean", and in actuality, I am performing disk cleanup on my own just about every day (mainly having deleted EMails permanently removed). Also, I have well over 60% of free space on each of those SSDs (and I do not do much "serious" processing with either machine, especially in comparison to you). I have always updated to the new Mac OS each time, although I wait until all of my third party applications are compatible with the new OS (and I have 6 critical ones that must be compatible). I have also done the upgrade from one Mac OS to another via a clean, fresh, "virgin" installation of the new OS. High Sierra is somewhat slower than Sierra, mainly in booting up, switching start up devices, switching to Tech Tool, Pro's eDrive, and then back from any of those sources to the internal SSD, and shutting down.
I also do not see anything drastically different and/or improved from Sierra, so unless you see a compelling reason to upgrade to High Sierra (like a new feature), it might be wise to upgrade to Sierra. Sierra is definitely a stable OS, and in some ways, I wish I was back on it. But I am getting more and more used to High Sierra, but again (at least for me), it has nothing earth shattering that is different from Sierra.