One huge advantage of the DCT M3 will be that it has 7 gears, allowing shorter spacing between gears, quick and seamless shifts, and still a reasonable cruising gear. I agree 1st gear should be reasonably long in high HP cars, and I find BMW loves to use a short 1st gear for a snappy feel off the line followed by too big of gaps between 1st and 2nd and 2nd and 3rd. This could be solved by using a taller 1st gear, just slightly taller 2nd gear, and the same 3rd gear.
The DCT m3 could be 0.3 seconds faster than the 6-speed in the 1/4 mile with a 2-3 MPH higher trap speed, depending on just how fast it shifts and what gearing they choose.
Driving sideways: It's not faster, but damn it's more fun!