Difference in image quality between the 23mm and 18-55mm @ f/8 ?

Being in Australia I am tempted by some of the EOFY sales and Fuji cash back offers and am considering the 23mm f/1.4.

I know there has been a lot of discussion in the past about this lens but I am wanting some feedback about how it compares to the Fuji 18-55mm at F/5.6 and above.

The primary reason I am interested in the 23mm is for the 35mm effective field of view which I very much like for street photography. Usually I use the Fuji 27mm for this but find it a little long. So I often end up using the 18-55mm lens and then get tempted to use different focal lengths which kind of takes some of the fun out of using a primes for street work hence I started looking at the Fuji 23mm.

Besides the fact that that it’s a prime, which I like for street, I also want the images to look as good as possible. Given that I mostly shoot at f/5.6 to f/8 on the street I got interested what, if any difference there is in image quality between the Fuji 18-55mm and the 23mm at these focal lengths.

If the MTF’s on Photozone (below) are to believed, not very much. In fact the 18-55mm is actually a fair bit sharper at f/8. Obviously there is a difference at wider apertures but for the sake of this discussion I’m only interested in f/5.6 to f/8.

Fuji 18-55mm (MTF)

http://www.photozone.de/fuji_x/783-fuji1855f284?start=1

Fuji 23mm f/1.4 (MTF)

http://www.photozone.de/fuji_x/868-fuji23f14?start=1

I'm surprised by this as usually primes are sharper than zooms so it's kind of putting me off buying the 23mm. I might as well stick to the 18-55mm and maybe just tape it up at 23mm (or at least exercise some self control with the zoom ring).

So, for those people out there that have (or had) both lenses, how would you say these lenses really compare for this scenario?

Is there something different about the image characteristics (not just sharpness) of the 23mm compared to the 18-55mm that makes if better in some way, even if it’s not as sharp?

Are the MTF values above just incorrect somehow?

Cheers,

Michael