... an update on the discomfort issue.
I took a look at the saddle after feeling like muscles on one side were strained during a climb, and found it was rotated slightly. Not sure what caused that.
I also tried reversing some changes I'd made a while previously. I'd tested them but on reflection I realised that a lot of riding around London involves stopping every couple of miles so something feeling like it was good wouldn't necessarily still feel good after many miles without stopping at a junction. I also corrected the saddle being slightly rotated.
That also meant that my sitting position was more comfortable. Previously if the saddle was uncomfortable I thought it meant the pad wasn't correctly positioned, and I realised I was tending to pull my shorts up tighter than was appropriate, so effectively by the time I got to the end of a ride I was cycling with a wedgie. That makes some of the pain far more understandable.
What I've got now is still comfortable after 40 miles (the furthest I've been since the adjustments) when most of that distance was on open roads without having to constantly stop. So now I need to ride one of my 200km routes and see how it all measures up.
Honestly I find KY or any other water soluble lube to be ideal for reducing friction down there. The stuff doesn't lead to an overgrowth of bacteria and your skin can breathe. Sweat provides the necessary moisture to keep it sliding once the bulk of the KY has moved to the pad. Wet Wipes if you want a mid-ride clean up too.