New MacBook or MacBook Air?

My good old beloved MacBook Air, purchased at the early phase of that model (Spring 2008) might need to be replaced soon (if I can't manage to fix its broken hinge by myself, since I was told by the Apple service that they do not longer repair this problem).

So I am looking quietly at the possibilities for replacement. Which is going to be -unsurprisingly- another Mac portable computer. And taking into account I use this computer for presentations,  and don't need a powerhouse, my shortlist is really short: either a new MacBook, or a 13" MacBook Air (as I want the bigger screen).

This comparative review posted by MacWorld is quite informative to take a decision. I have been digging at the Apple store with education discount, and found out that the price of a MacBook (with the Core M 1.2 GHz processor, 512 Gb of HD and 8 GB RAM) is roughly similar to a MacBook Air (with an i7 2.2 GHz processor, and te same HD and RAM).

So now, my only question is whether the difference in performance of the Core M vs i7 processors is significant enough for my uses: presentations, word processing, net browsing and occasional use of scientific graphics software. My guess is "no", but I would like to try by myself.

(And now that nobody is listening, I admit I have a very soft spot for the extremely sexy MacBook design and its overall philosophy, which is obviously the next logic step, after the original MacBook Air design.)