If you use a RW CD or DVD, you will automatically get a lower speed, usually about 4x
--I usually find that even running at MAX; most of the time with a RO CD, I can get a good boot, so I often don't even bother with a RW CD, since I am getting very few CD coasters (unusable media for boots)
It also sometimes helps to pick a DVD or +R, instead of other types for reasonable chance of a good boot
You shouldn't need such a low write speed to get a good boot, unless you have really old hardware
Even if you have a writable (rw) cd drive, then even if it is older, like 10yrs ago, it probably should still be ao as a bootable media device..