Backup from HD to CD-R

[mystvearn]

I want to backup lots of files, massive size. I have bought 100 cd-r that can support 48x. My cd-rw can support 40x. What is the best recording speed? Slower than 40x? or max speed?

I have had trouble when making audio cd's where after a few times using the cd, I hear this noise in the background. It gets worse, and there are cases where not all cd player can play the track. It only affects individual tracks, I'm not sure its because of high writing speed. Does it?

[Nuclear Krusader]

Audio CDs must be always burned at low speeds. Like 8x or 12x.

[glc]

If you are burning data, burn it as fast as it will burn. If you are creating audio cd's, keep it slow.

[mystvearn]

opposite speeds, odd. Ok.
Why is that so?