For those tempted there's a Sony 50mm f1.2 in the for sale section for £1,450, boxed and including all the normal stuff and including postage. The seller says it's been used 2-3 times.
In all this I think that focal length and perspective and the potential for blur and how much depth we want are all worth thinking about.
For eg if blur is the point then 50/1.2=41.6 compared to a cheaper 85mm f1.8 with 85/1.8=47 but here perspective and the nature of the blur have to be taken into account.
Oh. And a PS.
The widest aperture (f number wise) lenses I have are the Voigtlander 40mm f1.2 and Syoptic 50mm f1.1. For me there's a testing/honeymoon period where I want to see how it performs at various apertures and distances and after that the very widest apertures will only be used now and again and will be a small percentage of shots taken. Fair play to those who want to take every picture at the widest available aperture, I see the appeal.