Samsung combo drive is slow

I have the 1492 model Samsung combo drive. It supposedly reads CD-Roms at 52X. However, in practice, it is much slower than my BenQ 1620, which is rated at 40X. These drives are on the same IDE channel, the BenQ is the master and the Samsung is the slave. UDMA/33 is enabled for both drives.

So why would the Samsung be so slow? In iTunes, it could only muster an estimated 10x and would spin up and down between songs (always starting a song at 4x and jumping up to 10x halfway through) while the Benq pretty much just spun up to 20x and stayed there.

Any ideas appreciated!