I did some straight-line speed and acceleration tests at monza, from the start of the main straight from standstill. Rear wing in all cases is 1, increased gear ratios for each gear 1 click up. Set TC on high and auto box for consistency. First reading is as I cross the start/finish line, second reading is the white line that goes across the road just around the first of the braking boards for T1.
BMW: 203 232
BMW E46: 203 232
Chev: 206 232
Seat: 203 230
Alfa: 205 232
Honda: 204 231
Not too much difference then in a straight line it would seem. All down to handling for the lap times then.