As CCC doesn't currently work under Tiger, I used Disk Utility to clone my data to my new HD. CCC used to work perfectly, and Disk Utility appeared to run fine, but when I booted from the clone, the var, tmp and etc folders were visible in the Finder, rather than being invisible. All the data was there and everything was fine apart from this problem...but, it annyoed me, so I decided to boot from a Panther partition on an external HD and re-clone using CCC. I think this was just a bug, so it's relevance is somewhat lacking, but it's late and I'm awake so there's my anecdote.
As far as flexibility goes, I've never really messed around in the options of CCC, because I've never needed to - it works; never used Retrospect so can't comment on that.
The size of the clone HD will be however big the new HD's capacity is, for example, my disk was 120GB but only 80GB of data was on it, so 80GB of data was cloned to the new 129GB drive (I could have cloned this to any drive over 80GB) but the remaining free space remains available.
I believe the same is true for a Disk Image file (which I think is what you're really asking); the image will be 40GB and could be restored to any disk which is 40GB or over.