Have you seen this Wrotniak's lens comparison He compares those two lenses under identical conditions and shows a lot of samples.

My personal opinion is that within its range you will be hard put to tell the difference between the 14-54 and the 12-60, however the 12-60 might be worth it for the extra reach but only you can decide how important the last Ł300 is to you.

I have the 12-60, and am well pleased but as I only got it about 10 days ago I am still feeling my way.

Roger

Edit: Note that the 12-60 is big enough to throw a shadow when using the pop up flash - this might be a dealbreaker if you do not have one of the external flash units