I would get the Sports Differential before the B&O as Yes it makes that much difference in all but eliminating understeer.
Am hunting a 2010 S5 - I see some have a sport differential.
Does it really make that much difference in handling?
Any other "must have" options to look at? I like the B&O stereo for one ...
2012 S4 3.0T - Premium
2007 A3 DSG 2.0T - S-Line
2004 S4 V8 - 4.2
Had: 2000 A6 4.2, 2000 A6 2.7T, 1986 Coupe GT