Hi ELF, if you try Burrrn as I suggested, it’ll burn at 16x by default so no need to fiddle about with speed settings.
Reason I’m suggesting it, is it’s a lot simpler to use than Nero - just drag and drop your files into the Burrrn window.
As for Nero itself, I believe you can adjust the speed under the “Burn” tab of the “New Compilation” window. 