Sorry, but this will never work. Slowing down footage to 5% of its original speed will require any plug-in to synthesize 20 frames for every original source frame and at the same time doubling the framerate will also double that number. That is simply insane and inevitably since there is not enough information, any interpolation will have nothing to work with. this has nothing to do with what tools you use, it's a simple mathematical certainty. You are expecting too much and have a wrong understanding of the underlying principles. As a rule of thumb you can slow down footage to 30 or 25 percent of its original speed without too many artifacts, but anything beyond that is more or less nonsense.
you could try doing two smaller changes one after the other after a render. 30 to 45 then import 45 back in and render to 60fps.
twixtor pro has mattes you can isolate forground and background similar to roto. if that fails, i'd start looking to rent a terenax or alchemist OD if you want decent quality. they measure the final result to remove errors.
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