The proportions between DVD and CD speeds are totally different. A 1x CD is fast enough to play a cd without skipping. This speed transfers MUCH less data than a 1x DVD which needs faster transfer rates for video. The 1x is in reference to the speed it takes to play the media without skipping.
The faster you burn, the more unreliable DVD's become. the depth of the grooves gets less and less with faster burn speeds. No matter how fast burners get, I'll stick with a relatively slower speed for important burns. Also, if the end of DVDs is coming (Blue Ray, etc.) people are gonna pissed b/c of the slow speed of burning 40-50 gigs on a dvd. People are just never satisfied.
Comments
CD:
48X (7200 KB/sec)
40X (6000 KB/sec)
24X (3600 KB/sec)
DVD:
16X (21,600 KB/sec)
Thus, CD base speed = 150 KB / Sec
DVD base speed = 1350 KB / Sec