UPDATE: POLL added regarding drone. Please vote.
One of the advantages to having multiple M3s at my disposal is the ability to make live comparisons.
Today, I had my wife assist me with comparing her unmodified stock exhaust with valves closed to my M3 with the exhaust valve mod (valves locked open). This used to be called the golf tee mod back when I had my 335i.
There is a noticeable difference but nothing crazy it seems. Hope this helps someone deciding whether to do the mod or not. The best thing is that it takes literally seconds and is easy to restore if you don't like it.
I just added this one today...cold start comparison of no mod vs exhaust mod:
Added 12/15/2014: Interior view cruising, Light acceleration, cruising with stereo:
Added 12/20/2014: Exterior view accelerating at part throttle comparing wife's unmodded F80 and my F80 with the exhaust valve mod:
How to do the mod:
This is directly from the sound engineer responsible for the F8X and may indicate why the poll shows a lot more drone reports from DCT-equipped cars:
"There are also ranges in which we have chosen to close the valves, for instance at low engine speeds in high gears. In these ranges, which are frequently selected in the automatic mode of the M DKG Drivelogic for driving at maximum efficiency, the exhaust tract in turbo engines would have a tendency to drone if there were no damping."