Hi Simon, the car is my classic 1976 BMW 2002.
I was going to get the 23mm but I have to tell you I am so impressed with the 35mm and the 18-55 I may not bother. I read a blog somewhere the other day which compared the IQ at 23 mm on the 18-55 against the actual 23mm lens and to be honest there wasn't that much in it.
Only catch is the 18-55 is at F3.2 at 23mm and the 23mm will be at F1.4, from what I read the 18-55 is as sharp as the X100s 23mm, ime testing both alongside the 23mm is quite a lot sharper at F1.4 than the x100 and x100s are at f2.