This is not a direct answer to your question, but something that should shed some light. My 2000 ES sedan has OEM tire/wheel size of 195/55/VR15, and when I was living in new york even that size had a choppy ride on those horrible roads.
Anyway I used the tire size calculator on Miata.net, and downgraded to 195/60/HR14 for the winter. Of course, the speed rating and performance potential of these tires is lower than the OEM fitment (you will experience something similar but less drastic, since you can still find decent V-rated tires in 15"). However, the ride quality has improved substantially, with only a 0.5" increase in sidewall, and road noise has also decreased significantly. My guess would be that much of this improvement can be attributed to the softer sidewall of the H-rated, all-season tire, and the less-aggresive tread design.
So the take-home point from my experience is that downgrading can surely enhance ride quality but at the cost of performance. You can expect to have slightly more flex in the sidewall, which will make the car's body roll feel more significant, and overall traction may decrease a notch.