Sorry, mattyboy, but acko has given you good advice. If you want to learn, it helps to be open to advice, and not reject it because you want to be right.
Burn speeds allowed are determined by chipsets, firmware, and media. Software does not determine burn speed even if it lists a speed not supported. If an unsupported speed is selected, the actual burn speed will change to a supported speed. Software just allows the speed capabilities already present in the chipset, firmware, and media to be performed. It can’t override or change them.
There is no point in burning at 1x, but it can be done with OPTODISCK001 DVD-RW media rated at 1x. I got five of these discs free when ordering media. This media is limited to 1x on NEC and Liteon, but the BenQ 1620 will also burn it at 2.4x. Actually, it burns O.K. with decent quality but who has the patience.