Reducing Content DB size with Move to a new DB, best method?

I have a 2010 site collection content DB that swelled up to almost 300GB. About half of it has been moved to another site collection / content DB, but the mdf/ldf file sizes of the original have not changed.

I want to reduce the size of the DB. Thought is to

• create and mount new ContentDb2
• move the site collection using
  Get-SPSite -ContentDatabase ContentDb1 | Move-SPSite -DestinationDatabase ContentDb2

which, I think, should trim out the unused ContentDb1 space, making ContentDb2 half ContentDb1 file size. At the application level I'd then dismount ContentDb1.

Concern I have is minimizing lockout downtime.

• Move-SPSite is basically a ctrl X, not a ctrl ctrl c, correct? ContentDb1's data should be wiped out at completion?
• Copy-SPSite: is this available in 2010?
• Backup/Restore-SPSite: Assuming this would be the slowest. I'd have to prevent users from changing data during the process anyway.

Does this sound about right?

Thanks