Hopefully I can shed some light here,
DVD's of any RW type always have a smaller capacity than a standard R, It allows for rewriting of the disc multiple times, hence the strange size errors and nero informing you that you don;t have enough space on the disc, because you don't. The image you're burning is of a full size optical disc, not one allowing for overhead to be rewritable.
In fact, any kind of RW is shit for anything you plan on archiving long term (or spoofing a game console into thinking it's a real disc for a while, read around these forums you'll find plenty of "MY DVD+/-RW BACKUP STOPPED WORKING AFTER 2 DAYS HELP!!!!1111" topics and you'll see what I mean.) they're meant to be the optical disc equivalent of a floppy to get about 10-15 uses out of then trash, certainly not the high intensity use you;re trying to get out of it. Not to mention it's common fact that some older disc based game consoles needed laser adjustment to read those type of discs as well, which is already enough to make me not want to use that sketchy format.
Anyhow, figured I'd offer my 2 cents so everyone stops trying to figure out if it;s the burner. It's the media and the media sucks, use -R. 20 Successful self backup and burns without any problems. Run of the mill LG dvd burner (not the one that reads wii originals, used Wifi) decent sony -R media bought in a spool from a wholesale store, nothing special, and used IMGBurn.
Good Luck
EDIT: And if you have to use a +r Drive, try setting the booktype to DVD-ROM in IMGBurn.