The performance of either the LS or non LS 28mm is about the same, as there is no difference to the layout of the elements.
On a P45+ with the 1:1 crop, I found the 28mm (Mamiya version but again the same lens), ok from F11 to F16. I am always looking for a wide view that is corner to corner sharp, with little smearing/noise. The 28mm will smear pretty badly from F4.5 to F8 and then it starts to get better, again this is on the P45+.
On a 60MP back, the 28 shows that it really can't keep up at all until around F14 to the corners. What was soft in the F4.5 to F8 range on a P45+ is now smeared and worthless, requiring a crop to about a 1:3 size. As has been said many times, the 28mm on a full frame back is a great 35mm lens. And I agree with that. Also if you take it much past F16 you start to get diffraction softness so it's a very narrow range.
The lens is not filter friendly, not sure if you are a filter user. Requires some form of a modified Lee or Cokin holder unless Phase One did ship the custom filter holder that was mentioned at Photokina 2 years also. I have never seen any mention of it so not sure if it ever became real. It looked like it was made by Lee and was similar to the SW150 mount they make for the Nikon 14-24. Looked like it would hold 2 filters.
The DT comparison between the 28mm and 32 Rod is also pretty telling. It's worth looking at.
As mentioned already, the 32mm Rod is the overall best performer, if you go tech, but it's very heavy, delicate, and of course expensive. Based on the results I looked at from the DT IQ1250 testing, the shots would have definitely benefited from having the CF installed and for that add another 1K or so.
New the LS 28mm is cost to 4.5K last time I checked.
I have the Rod 28mm, love it. Excellent lens only limited by the 70mm image circle and the built in vignetting device, which you hit on a full frame sensor at around 6mm of shift. The lens would easily go to 10mm maybe 12mm if Rodenstock had no placed this hard vignette edge inside the lens. Never will understand that.
Paul C.