text: I recckon converting DVDs to an AVCHD would mean getting better quality at a smaller file but I doubt it for Blu Ray.
  What that's telling you is this: you can put as much running time as you want on a Blu-ray or AVCHD disc by using lower bitrates. But the lower the bitrate you use the worse the quality. You have to decide for yourself how much quality you are willing to lose. And you have to do that on a case by case basis -- different videos require different bitrates.
  There might be an opportunity to re-encode DVDs with a difference AVCHD compliant codec that might save you some space without quality loss but Blu-Rays will likely lose some. It might not be noticeable though...
  save as data ? it doesn't matter which compression you use, most codecs are supported, only no fancy menus, only file structure on screen.