Ok, so after a couple of weeks of running the Megan's I can say that I am very pleased with their performance. Definitely stiffer than stock but not overly harsh. Handling is greatly improved, some of which can be attributed to the Tri-Point Engineering rear sway bar installed at the same time as the springs. The whole family has ridden in it several times and I've had no complaints about rough ride. The Megan's leave enough suspension travel in the rear to keep the ride softer for rear passengers. The springs did take a few days to really settle in, those first days I was a bit concerned they were going to be too harsh. They softened up though and I'm very happy with the ride and handling of my sport van.
Below are my ride height measurements as requested by a fellow member:
Mazda RX8 18" wheels = 19.56 " (496.89 mm)
L/F 13.73 (343.7 mm) // R/F 13.61 (340.5 mm)
L/R 14.48 (362.8 mm) // R/R 14.48 (362.8 mm)