My perspective on the springs is biased by the fact that my 2 prior cars were a 2008 M3 and before that a 2000 M5. Although the M3 was a thrill ride and blast to drive, it was a little hard on my back and butt on rough midwest roads, especially in the winter. Then I test drove the stock 550i and I thought it was a bit like being on a boat in water when I turned corners sharply. The Dinan springs took the roll away but did not significantly roughen the ride in my view - I think by the way, that any roughness in the ride has more to do with the OEM all-season runflats that came with the car - I'm probably going to change them this summer to Conti Extreme Contacts. As far as the exhaust - I love the note. It is a bit throatier than the M3 but not overdone - I like it. Might change the tips though - or perhaps a diffuser. I could get carried away - my next cosmetic thing is to get an M grill.
I think some M drivers wonder what the point of all this is - M5 doesn't come in AWD. This is about as close as you get to an M5 with AWD. Just watch, though - the MB E63 AMG is coming out in AWD next year I believe. AWD M5 is just a little while away I suspect.
Current - 2013 550i xdrive M sport carbon black Dinan S2, Dinan suspension, Dinan free flow exhaust
Retired - 2008 M3 space gray
Retired - 2000 M5 carbon black