Are you going to be using the factory headunit? If so, upgrading speakers won't make any difference.
You'll find that the standard speakers will actually be louder because they are made out of paper and have a higher sensitivity, meaning that they can make the best use of the little power your headunit has.
Even if you have an aftermarket stereo, you'll find that replacing the speakers won't make much difference either. Although most HU claim to be 4x60w, this is a max figure and it is ulikely it will produce anything over 20w rms.
Remember, amplification is the limiting factor, it determines how loud your speakers will play, and in my opinion unless you are going to add an amp, changing your speakers is not worthwhile.