In short, I am unsure as to whether there is any research on this matter.
Most of the posts here concern 'what works for you' type scenarios in which you are riding in mixed ability groups in various conditions. However, I believe you are asking a more theoretical question and whilst I do not know the answer, I will give my opinion.
The efficiency of a paceline determines its ability to maintain a certain speed. This directly results from the energy expenditure of the riders. As such, a given rider will expend more energy the longer he is at the front or accelerating to rejoin the back.
I see this issue as a trade off. Shorter pulls mean less time at the front, but more frequent turns and more time (overall) spent accelerating to rejoin the line when the last rider goes through.
The benefits of longer turns are: longer recover time between pulls and less frequent accelerations at the back. The obvious drawback being that each turn is more tiring. If a rider is dropped from a TTT, I would suspect that this has a greater impact upon reducing overall efficiency than the length of turn.
This leads me to believe that it's more of a question of fitness of the group, assuming that the formation is equally as tight irrespective of whether the turns are long or short.
Given that in pro races, all riders are exceptionally fit and roughly the same standard (unlike a category 1 rider doing a club ride with a category 3 rider), the time spent at the front equals the total ride time divided by the total number of riders. Therefore, the total time each rider spends at the front is the same. One thing that has been overlooked is that when the group is towards the end of the race, each turn takes a lot out of each rider. This may be why pro teams tend to favour quick rotation rather than long turns as pro riders may be able to withstand short bursts better than sustained efforts when they are close to their aerobic threshold.
Certainly not a definitive answer, but hope you found these comments interesting.