I read the research being done before introducing the breathalyser. The tasks were mainly tracking radar plots. The amounts of alcahol weren't large but subjects were not as aware of things happening. They tended to concentrate very hard on what they were doing rather than what was happening if you understand what I mean.
I have certainly driven pissed in the dark past and I have driven (and flown) knackered. I did things very well when pissed but I didn't react to other things quickly, such as people stepping out or other traffic. Being knackered was def. bad. I rolled a motor once after after a long stint. I didn't realise how fast I was going and was frankly sluggish.