I suggest to get a more updated burning software (DVd Decrypter is not more updated by years).
ImgBurn is certainly an excellent option (it is actually my suggestion :iagree:)
btw, the burning speeds available for a specific media are determined by the firmware, not the burning software. Reducing a bit the burning speed can improve results, but it cannot transform a bad disc into a good one. The main solution is still to get some Verbatim media