Can you preview a song in iTunes Match before upgrading your local copy?
If you move all your songs that you are about to delete to a different directory, iTunes should no longer be able to find them, and you should be able to hear the matched version and inspect its encoding. If you regret it, it should just be to move the songs back to where they were.
Haven't tried it myself to test it with one or two songs first!
You can delete the reference to the local file in iTunes by deleting and selecting "Keep File"; then streaming or downloading the song from iCloud won't touch your original file.