Well I did some back-to-back tests today. I didn't get to do all the tests I wanted, but this will give you an example of what these cars will do on the same day, on the same road, with the same driver.
Information about the testing:
It was 85 degrees this afternoon (this is crazy for mid-January). I've done much better times with all these cars on colder days, but the point was to get side-by-side comparison numbers.
It hasn't rained in weeks, so the road was a little gritty. I didn't get solid launches in any of the cars. The M3 was probably the least affected by this. The M5 was the hardest to launch effectively because it would light up the tires with a full throttle launch in 1st no matter how I did it.
I turned DSC off on both the 5's. I did not power-shift (i.e. keeping it floored during shifting). All the cars were between 2/3 and 3/4 full of gas.
I made 4 runs with each car and averaged the two best times. The max G in each gear was done after the 0-60 runs. I just rolled on the throttle in each gear and took the peak G achieved between 2500 and 5000 rpm.
M5 540i M3
0-60 5.1s 6.2s 6.2s
1st 0.70g 0.57g 0.55g
2nd 0.55g 0.42g 0.44g
3rd 0.35g 0.28g 0.28g
Note that the M5 pulls just as hard in 2nd as the other two cars do in 1st!
(FYI, with cooler temps and better traction, I've gotten upper-mid 5 second times in both the 540 and M3 before)