NEX-5N with kit lens vs. Zeiss lens

I have been using 5N for half a year now, and I want to know how much of an improvement in IQ is a more expensive lens like Zeiss compare to the kit lens (18-55mm). Are there any photos comparison that I can use as a reference?

Edit: it doesn't have to be a Zeiss, I just want to see what difference can a better lens make on the 5N, it's something worth knowing before I spend the money.