If you only have one active Poser folder (and the other ones merely for reference), then definitely go for the ExtraRuntime model. Best start one last time with a clean installed Runtime, and then just add everything into ExtraRuntime. Whenever you have to switch, drag it into the new folder and select "Register", that's all. This is exactly what I'm doing - I now have a nice growing pile of 7 CD-R's containing different Poser version folders, and whenever I exchange my current one, it takes less than a minute for Macinstaller to get my tons of custom stuff recognized as it was before.