I've only been vaping for less than a year, but I think you get more medication from sipping medium vapor for over 10+ mins, than you would taking a few lung-busters of super thick vapor. The initial effect might seem like the lung-buster is better (you know, that dizzying-gonna-pass-out-coughing type of hit that feels like an old fashioned bong hit), but that bit of oxygen-deprivation followed by hyper-ventilating passes quickly.
A good example might be bags. I can fill a bag of thick vapor with my Rise, and some friends feel like they will get higher if they try to take the bag all at once. They cough and wheeze and then look like they are gonna pass out, while I slowly sip on my bag. 20 mins later, I seem to be more medicated than they are.
I think there is a limit to how much you can absorb in a single lung-full, and if you go past that limit, you're just throwing away vapor. So...I think that slowly taking in many hits over 5-10 mins assures that every hit can be fully absorbed every time giving you the highest quantity of meds.
As
@stickstones says, eventually someone will study this and we will now for sure.
I did find this study (they used a Volcano):
http://onlinelibrary.wiley.com/doi/10.1002/jps.20574/full
" It was found that an average of about 54% of loaded THC was delivered into the balloon of the vaporizer, in a reproducible manner. When the vaporizer was used for clinical administration of inhaled THC, it was found that on average 35% of inhaled THC was directly exhaled again."
I also recall a study (Hightimes I believe) indicating that 100% of lung absorption occurs in the first 3-5 seconds, and "holding it in" is not effective at increasing that absorption rate. If true, this also seems to indicate that there is a maximum absorption rate.