What are you using to burn the DVDs? DVD Shrink will allow you to re-author the original and strip out any unnecessary stuff so as to reduce the compression required for a single-layer DVD. Sorry if this is old news. Just curious.
BTW, count me in! I have about 30 blank Memorex 4x DVD-R discs that my Plextor suddenly refused to accept gathering dust. Yours if you need 'em!