My car is S2+ making 351bhp. Its hard to compare with the speed because The highest gear I got into was 3rd. Up until 3rd my car wouldnt stand a chance, it really covered ground quickly. I cant see it being any faster after or during 3rd though, it cant be. Would be an interesting race.
As for a comparison to DSG, my car is manual and the only DSG car that I have driven is a new Polo GTI with the 7spd, which is very impressive, but what I found better with the AMG is full control of the gearbox in manual mode, it will not change gear unless you pull either of the paddles. For that reason only I think it was better. Appart from that the gear changes just seems the same, the speed of shifts and smoothness etc.
I cant compare to the 6spd DSG in the golf though as I have never been in one sorry.