im burning taiyo yuden 8x dvd+r using dvd decrypter on my dell 8400 with the stock dvd burner. i select 8x in dvd decrypter but it starts burning at like 3x works its way up to 4x fluctuates between 4x, 6x, and then near the end stays at 8x. the average write rate ends up being like 5.5x. why? also if i backup an iso image from an already burned dvd...what should i rip it with, right now im using decrypter but that seems unnecessary right?