How long... almost 2 months now. I'm using esata, usb is stuck @16x at best.
The buffer is fluctuating "normally" during the 22x burn, no burning problem (check esata controler, I'm using Intel ICH9M esata port, no problem with it, but some jmicron are crappy...for exemple), burning quality is the same as when the drive is used "internally" with a good power supply, whatever the speed choosen (except 24x, I only tried once, and burned failed)
Isn't 12V mainly used for the spinning motor ?
With AD-7240S series, the maximum burning speed of Verbatim 16x is 20x for the moment, you have to use TY to reach 24x (and IMO you'd better chose 16x speed)