[gh0sth@cker]

The software may or may not automatically adjust to correct speed, however ultimately it's the drive's firmware that decides what speed to write at.
If you buy a 2x disk then your drive will only write to it at maximum of 2x - you can get hacked versions of the firmware to write at higher speeds but it isn't recommened as the disks have a speed rating for a reason. You will likely encounter errors if you try this.
If you want to write at higher speed then buy some 4x disks