These guys got a 12.8@108 with their tune. I'd hope for similar numbers.
The feel of noticeable slowing after the first two gears is true for the the X5M as well, due to weight, frontal area, and drag catching up with it. It's just the nature of the beast. It's fastest off the line due to gearing and traction. The X5M does 0-60 in 4 seconds vs. 5.1 for the 550i, but the 60-130 times are identical, and after that the M fades. That's a lot of frontal area to push through the air at 100+ mph.