Ok so had my first decent drive of the car this afternoon, as I took the long way home from work. Here are my initial thoughts on the handling.
Sports exhaust: has a sporty but restrained note. Noticeably more sporty than standard but not 'in-your-face' loud if that makes sense.
Gearbox: Eco mode is as per the AMG Sport I test drove. That is to say it is quite docile, but smooth, taking off in 2nd unless you max out the accelerator pedal, and short-shifting to save fuel. Sport Mode is a marked difference. The car feels much more eager to move away when you release the brakes and the shifts are delayed upon hard acceleration. Downshifts generally smooth. Manual mode I tried for the first time tonight on a twisty B road. During spirited driving the up shifts are almost instant, although ever so slightly slower (and understandably so) in comparison to some double-clutch systems I have previously experienced. The downshifts are entertaining with the car actively blipping the throttle as you change down, adding to the sporty feel and giving a nice aural experience. The downshifts generally happen as requested, though don't expect the box to change down if you are endangering the box and engine by requesting a change which will cause the engine to over-rev.
I should qualify my opinion by saying that this is the first auto I have owned. I have completed various advanced driving qualifications at work and was worried that I'd miss the involved feel of a manual and the satisfaction of nicely executed sustained rev changes etc. I shouldn't have worried as I still found the auto engaging in manual mode, and the active downshifts put a smile on my face.
Handling: in general I have been very impressed. The suspension is firm but the car absorbs bumps in the road with class and ease. My previous car was a 330i m-sport which crashed over the bumps by comparison. I much prefer this car. It maybe doesn't have the dynamic handling some associate with BMW but I am more than satisfied with the car and can't fault it in this respect.
Hope this helps.