According to a Japanese site WatchImpress (I can't remember the URL), they tested both 14-45 and 14-54 lenses.
According to them the 14-45 kit lens is sharper than 14-54. The kit lens is a must buy for all E-300 potential buyers. That said, the 14-45 even slightly slower, but it's a very good lens after all.
I'm very satisfied, and lucky to have bought this kit, saving up for other lenses and forget about the 14-54.
I've just got the 50mm F2.0, and I am really impressed! :thumbsup: A must-buy too.