Webwork - 2:37 pm on Jul 29, 2011 (gmt 0)
The issue your raise is so granular that I would be very surprised if you found an answer "in the wild". Why? Because answers to questions such as this, though they may exist, often come at a very high "experiment and burn" cost and therefore the results of the analysis are not made public.
In the emerging scheme of SERPs-things I'd say investing further time on this issue won't yield a payoff worth the further investment . . . buy ya never know.