CAV is Constant Angular Velocity. Drive motor speed stays the same and the throughput increases as the optical unit moves outward. The larger circumference means more data moves under the head as you move further out. Gives a linear curve from min to max. CLV is Constant Linear Velocity. Motor slows down so the data rate remains constant. The 40X is Z-CLV. Starts at 24x, jumps to 32x if the media burn is ok, and then to 40x after checking the media again.
PoweRec checks the media quality. If crappy, it keeps the drive from jumping to the higher speed and writing with a high error rate. Along with burnproof, you can use crappy media and still not produce a coaster.