I spent a lot of time today riging and re-rigging the 5.2m Koncept, as this size is my Prime speed size.

I tried it on 3 different RDM 370 masts. (One was standard KA. Another, a mast built in the same factory but a few mm smaller in diameter (called Ultra RDM), the third I sourced from another factory to my specs) All identical in measured bend curve but slightly different in diameter and stiffness.
Read on keeping in mind I am getting
very picky now:
All looked fantastic and honestly, I would be perfectly happy with any of them. But I think I will use the slightly softer one first so see it I get slightly better 'feel' in the sail.
The specs on the sail are spot on for boom length, and maybe a cm long for downhaul. You could put 393cm on it but I liked it better at 391.5 -392cm. (Some, but not all, sails stretch about 5mm over the first few uses. After that they don't seem to change.). For the Luderitz canal, I would probably go to 393cm.

I think this 5.2m looks to be slightly more of a dedicated speed shape than the 4.7m and 5.7m. It appeared slightly deeper and more twisted. Maybe that is just wishful thinking, but for what I want that should be perfect.

Cam rotation was a bit tighter than the other two sizes, which is also a plus for speed but I did some 'tuning' to get them rotating easy as well. For most sailing I prefer easy rotation over ultimate rigidity. They rotated easiest on the skinnier, ultra RDM mast so I will probably use that one for just blasting around.
The sail sets very clean as with all the other 2019 Koncepts I have rigged. The wider luff pocket of the Speed sizes looks really great and the bottom cam pushes noticeably more depth into the bottom of the sail and looks nice on the land.