Well, it's been a journey
Bought the Leopold FC750R w/ browns and liked it, but then got curious about some others, so ended up also buying:
KUL ES-87 w/ clears
Pok3r w/ clears
Leopold FC660M w/ blues
Leopold FC660M w/ browns
Leopold FC660C w/ topres
I knew I would be reselling most of them and would lose a bit in shipping, but wanted to give those boards and switches a try. I honestly thought the Leopold Topre board was going to be the one for me, but after using it for a little under an hour, I was pretty sure it wasn't. It was nice to type on, but definitely "slower" than my preferred mx-browns and just generally not enough of a step up from mx switches to justify the 2x price tag.
I did find, however, that the FC660 form factor is perfect for me and in the end, I settled on the FC660M with browns.
So now I'll revisit my initial question: build quality comparisons.
I can definitely say that the Leopold build quality is right on par with the Ducky Premier. The typing experience is almost exactly the same, to be honest (comparing the brown switches across all three - Ducky Premier, FC660M, FC750). Caps feel great on both, sound is roughly the same, and keypress is generally similar.
The only difference I have noticed is likely due to the cap profile. I believe the Premier has OEM profile caps, which are taller than the Step Sculpture 2 caps on the Leopolds (similar to Cherry profile). It's probably just a learning curve, but I have noticed lower accuracy so far on the shorter, Leopold caps.
Any who, just thought I'd give an update.