At the moment, I could be wrong, but I think you’re always going get some softening from the undistort round trip. That said, I have found action to get slightly better results than the matchbox. Also Nuke, as you probably my know, has different filters that might get a different result that works better. And doing resizes in log can avoid those horrible little negative pixels that get introduced by certain filters.
Also check this out. If it’s the @cnoellert setup I’m thinking of it’s pretty foolproof.