>Control over page generation being unclear "coloured" my answer as well. From performance POV there should be no compelling reason for either version: calling such functions in tight loops with last centuries HW was almost totally bottlenecked by internet speeds, not CPU load. Yes, bandwidth has grown stronger than CPU load and you clearly have a much better connection setup than I had - but having no idea on your CPU load distribution and percentage of page builds this functionality is called vs. "normal" page builds you would have to add the non-script-enclosing DIV tags, my SWAG guess would be adding DIV to ease/elevate structure comprehension to HTML level is IAC better compromise.
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>Should you decide to make the effort to measure, pls. post results: As I have no current expierince in that area, actual data from your end is always welcome. "Still irrelevant" today and in your setup being also a result worth knowing ;-)

This is in regards to everything that appears on top of the main container. This is like a pick list, a calendar selection, a view of a report, a color selection and such. This is also widely used on Facebook. This is all done with DIV now. So, the main container is responsible for creating a DIV and simulating a "new window" type while in fact it is not. So, it appears immediately as there is no new window involved, and closes extremely fast. However, to fill it in, another process has to do the job. Once the data received, the content is transferred into a newly created DIV, usually appearing centered or next to a specific object.