one main difference between CDR and DVDR writers is, a DVDR writer will need to have stored all burning parameters for every particular DVDR brand in his firmware;
if you buy media which your drive don't know (because it's firmware is older than the media release), then it will mostly end in a coaster;
you can update your drives firmware, so it should know how to handle your new 8x (quality) media; then you can use 8x media with your 4x drive (of course in 2x or 4x burning mode);
Greetings from
Duracell