> Has anyone seen any studies that have demonstrated a clear benefit from allowing them to lay for a longer period prior to caging

Just the opposite:

> Queens that have been laying heavily suffer seriously from the confinement in a small cage and the journey through the mails. Often they will never do as well for the buyer as they have done previously, and he is inclined to feel that he has not been treated fairly. As a rule, the same money invested in young untested queens, will bring far better results to the buyer, as well as being better for the seller. If a half dozen young queens are purchased from a breeder with good stock, at least one of them is quite likely to prove excellent. 

> The best queen that the author ever has known he secured as an untested queen at a nominal price. There is probably no extensive queen rearing yard which would part with as good a queen for fifty dollars* after she had demonstrated her value. In fact, she would not be for sale at any price, for she would be too valuable as a breeder. Yet the chances are that, after she had demonstrated her ability by outdoing everything else in the apiary for three successive seasons, she would be superseded within a few weeks after being sent through the mails. -- Frank Pellett

* This was written in 1917, when queens sold for a dollar. Breeders went for 5 to 10 times the value of production queens. So, he is saying one would be better to buy a bunch of production queens and select from them, rather than to pay a lot of money for a "tested" queen. This is echoed by more recent work by Tarpy and Delaney:

> Queen "quality" significantly varied among commercial sources for physical characters but not for mating characters. These findings suggest that it may be more effective to improve overall queen reproductive potential by culling lower-quality queens rather than systematically altering current queen production practices. 

Tarpy, D. R., Keller, J. J., Caren, J. R., & Delaney, D. A. (2012). Assessing the mating 'health' of commercial honey bee queens. Journal of economic entomology, 105(1), 20-25.

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