... although the 40w 2x12 sounds clean at low volumes,I haven't pushed it to the point of breakup inside,much.
I think although the Vibrolux would distort sooner,they have with what little experience I have had with them.
I guess it's kind of funny, strange, ironic, whatever you want to call it. I've always felt the VR had more clean headroom than the DR.
Regardless of which amp one is using and what past experiences may have been one can always tweak the amp to break up slightly later or slightly earlier by way of power tube bias adjustment and careful selection of the rectifier tube. It's not going to completely reshape the tone but there can be a small but noticeable difference.
I think the more important issue is how a person wants their amp to behave regarding dynamics. That's where the true difference between these amps lies, IMO. The DR has more natural compression to my ears than the VR and as such can tend to be just a bit muddier. That's not always a bad thing as the DR is a much more forgiving amp in the hands of lesser skilled players. The VR is a much sharper scalpel with a significantly wider dynamic range. This can make the amp seem to be an "expert only" amp as it will make your mistakes glaringly obvious but will reward your precision and clean playing with a sweeter tone and greater expressiveness.