dreamcast problems and media choices???

I have started burning dreamcast games using my plextor 12x on tdk media. The discs work fine for a while, but then they just stop working!!! I can play the game for about a half hour and then it just stops working. The games I have tried are PowerStone2 and Tetris. The symptoms are the same for both games. Should I try using a better media???( Mitsui and Sony are supposed to be better than TDK - correct???).

Do you need 80 minute CDs for all dreamcast games? I have been using them - but was wondering if I could get away with 74min ones???

Thanks