I'm with you there. For seemingly big brembos, the stopping power isn't all that great. The good news is that I think it is 90% the pads, not the design or sizing. The pads wear extremely well and don't kick a lot of brake dust, at the tradeoff of stopping power. I think the brakes could be quickly improved with a more aggressive set of pads.
I've had lots of cars north of 130 and quite a few above 150 MPH on the autobahn, from sh!tboxes to luxury sedans to pure sports cars. No doubt, they all feel different - some are confidence inspiring, some are downright scary at speed. But I have always felt that much of the difference was a "sensation" of stability versus actual loss of traction or directional control.
Heck, my Lexus IS corners better, or *feels* like it corners better than the Maserati. But at 130-135, the Maserati feels plenty solid on straights sweeping turns, with a stock Skyhook (and always, of course, on Sport setting).
I'm going to test drive an S5 next week - it will be interesting to see how it "feels" different.