In my opinion, quick launch is required for drags. The 0-60 claimed by the company itself is usually with normal lanuch.
Usually in drags, the clutch is engaged first and then engine is throttled to the max. Since you have to reach the finish line before your competators, you won't want to loose the traction.....
Yes for 0-60, the speed gun would give you the exact figure about the speed, not even the speedo would do, since it shows the wheel speed not the actual speed of the vehicle itself!