My wife is 48 - 50 kilos (well, more after being pregnant) and I could feel the difference with her in the car. Oddly enough, the added mass is not as noticeable in the Miata.In my brief drive of one a few years back, I was with the owner and A/C was on. It didn't feel as slow as everyone said, and I didn't remember the NVH being terrible. But that would prob all come with time.
This should def address the power issue and I'd bet some of the added weight went to NVH mitigation. IDK man. Outside of badge, cylinder count and depreciation.... I'm struggling to think of reasons not to add this to the sports car shopping list. This checks off all the realistic new sports car boxes