The pressure vs extraction was an issue in the days when smokless powder first appeared and the brass was not quite up to the task. That's less of an issue with today's improved brass. On the other hand there's simply no reason to have high pressure if you are using a cartridge designed for a double. High pressure is only required when you are trying to use a bolt action cartridge in a double.
The rimless vs rimmed issue IS an issue. Rimless extractors are more complex and compromise reliability. Even without breaking they have the potential for a case haed to get under the extractor and tie things up.
Back thrust is a a product of both pressure and head area. Either one taken alone means nothing as far as action strength goes.
I've seen a side by side in 9.3X74R with kersten fasteners. This rifle was so light that I would have been afraid of the recoil. Which goes to show a double needn't be heavy.
