Hi kiaconcepts (strange name, you drive a Kia car I precume? ), welcome to the forums.
You say that you can burn DVD-R media at 4x but only with Nero and not with DVD Decrypter? Are you using the same media? If so then I don't really know what could be causing your problem since normally the burn speed depends on the hardware and not on the software (provided of course that you haven't manually selected a lower recording speed).
You can update your firmware to 1.06. My drive is running 1.06 and I have not experienced any problems so far. When you do experience problems you can always downgrade to a lower firmware again so this isn't really a problem.
8x DVD-R burning is not possible with the Plextor PX-708A, there is no hacked firmware that can enable this for the drive. The drive can run from an IDE controller. I also have four burners installed in my computer and they're working fine.