The ONLY time it's necessary (or even advantageous) to burn at the slowest speed possible is when you are using any combination of low quality media (think Memorwrecks and other cheap, no name blanks), cheap burner, or poor burning software. If you use a GOOD burner, and they can be had for $15 quite readily; good blanks like Taiyo Yuden, Falcon, Sony that are made in Japan (Sony's made elsewhere are junk), Verbatum with AZO Dye (their others are junk), and a few others, and good software like XFBurn, K3B, or IMGBurn on Windows then you will be better off burning at the disks rated speed (if the burner supports it) or no more than 1 speed slower. Forcing a 24X burner to burn 16-24X disks at 4-6x is foolish and will result in a LOWER QUALITY burn.

Honestly, this MYTH about burning at the slowest speed needs to be put to rest.