SRGilbert, I *do* use cd-r's as well. Notice I didn't complain about the loading time for cd-r's, only cd-rw's.
Also, I don't utilize packet writing or multiple sessions either.
Regarding cd-r's, I burn them @ max speed (usually 48-52X) and the IMP has little to no difficulty in reading said discs. In fact, recent tests have proven that burning at such slow speeds on modern burners/discs actually creates discs that are more error-ridden than discs burnt at a higher speed (say, at least 24X or 32X).
Jipi, I've only tested with one 24X cd-rw disc (which I believe is manufactured by Infodisc) that came bundled with my Lite-On burner. I need to track down some Verbatim discs, which come highly recommended as far as quality is concerned.