Drivers and voltage

I’ve got a question on drivers. Those that list 3-6v,3-8.4v and 3-9v etc., is there a voltage thats perferred by the drive? Example on a 3-9v listed one, what voltage runs the best on efficency, durability? Should I try to run at that voltage or just keep it in the listed range and not worry? Right now I’m mostly concerned with the single boards used in D26 dropins. Thank You.

I would expect that many of these drivers needs more than 3 volt for full brightness, maybe up to 4 volt.

If these drivers do not have a spec sheet showing the effeciency, then they could be very inefficient in certain voltages within the range. Some of them are still very inefficient at their "sweet spot". It all depends on the driver and it's components. Most don't have a spec sheet or a test sheet, but I know on DX (or used to be), that in the comment sections for some drivers, some people would list their findings.