agoldstraw,

Just a thought, take it for what it's worth. You apparently don't sing and therefore wouldn't need the vocal harmony feature. You might be as well off going to a lesser model such as the Korg PA600 or Yamaha PSR S-770 especially since this would only be used on some jobs (if I read the situation correctly). You wouldn't have to break the bank this way and you would still have a decent keyboard to use to back up a vocalist.

As for your question in general:

Korg-the perception is a more "live" sound than Yamaha. Recently, the opinion of the pros here (I am a home player only) seems to have swung slightly in favor of the Korg. Yamaha has the most active user support forums (although the Korg has a good forum as well) and the most styles available. Korg songbook feature is usually preferred over the clunky Yamaha registrations. As you say, you'll have to test drive both to find out.