Ok, well first off, I don't think Adaptec will let you overburn, but Nero will. Though overburning can damage your CDR physically, so I personally don't do it. Though to overburn 12MB of data is quite a lot, and I doubt you'll fit that onto a 650MB disc. One of your options is to buy an 80Min/700MB disc and that will burn on completely. As for overburning, it depends on the media and CDR drive though what you want to do is too much for the CD.
--Mark