Wait, how could Palringo make your iPhone run slow? You can't do anything on your iPhone while it's running except play music. Once you hit that home button, Palringo is no longer running on the device at all, not affecting anything about the iPhone.
You may want to tough it out with Palringo rather than spend any money on an IM App until Apple releases OS 3.0, as that's going to allow IM apps to make your phone alert you when a message comes in even while the app isn't running. You don't want to spend money an an App that doesn't end up supporting that.