Well, the Mach was my 9th Mustang through the years, and my second Mach 1 model (first was '04). Latest model owned was a 2013 GT/CS. Had everything in-between '69-'22.
Compared to the Blackwing, you definitely feel the weight in corners, but I'm still new to the car. It's planted and extremely confidence inspiring. Getting out of the Mach and into the Blackwing, it's a comfortable transition.
Low slung, hard to get out of, not the best visibility. Both V8, both Tremec 6-speeds, both RWD. Both insanely quick - more than anything needed on streets.
That said, even though the interior of the CT5 is absolute shit compared to my wife's Porsche and on par with my F-150, for the price, I'd have preferred better. I drove my Mach about 200 miles before I threw an MGW into it, and that is better than the Blackwing, but I feel the Blackwing is better shifting than the stock Mach 1 shifter (lots of time at the Mach 1 Track Attack school).
As far as driving dynamics, as long as you realize you're hurling a 4,100lb vs 3,800lb car around (which astonishingly is something looking at the boat the Caddy is) and given it has the 668hp vs 470hp... It's incredible. My wife's Porsche is a twin turbo V8 and the Blackwing is a supercharged V8. 4.0TT vs 6.2S. The power delivery is damn impressive considering the differences.
The Mach 1 was as linear as any NA V8. Loved it, extremely predictable. The Blackwing seems the same so far in the <200 miles I've had it for. But that's positive displacement with the blower. Low RPM grunt in a high gear is just mind boggling. But this is also my first supercharger car.