Thanks; when I bought this box last summer, the TB3 HDD drives they had at Fry's were WAY slower than the USB3 HDD drives, and FAR more expensive. They said the ideal was on paper only but might be met within a couple of years, and it seems that is now the case when I look at newer TB3 HDD drives, and that they are now price-comparable with USB3 HDD drives (which is now on the way out) or cheaper.
I'm not going to experiment with the internal drive as it identifies itself as an HDD under system specs, so I doubt any sector of that "hybrid drive" really and truly behaves (performance-wise at least) like a real SSD.
I'll check TB3 SSD drive prices and capacities after my rehearsal tonight, and place an order. At least 2 TB for sure, and way more if the price scaling isn't exponential and is instead rewarding vs. punitive.