OK I've narrowed it down to the following Yanagiba due to not being able to handle any of these knives I appreciate any views from people who own or have had experience with them;
Kochi 270mm - at JKI Helpful retailer who obviously chooses well.
Watanabe 270mm Professional in White steel, purchaed Deba in same steel - great service lovely product from a maker who from reading reviews makes very fine single beveled knives.
Heiji 300mm Professional Swedish stainless - lovely looking knife from a top maker so from my niave perspective I can't foresee any "problems"
If you've got the space, I'd say get a 300 rather than a 270. 30mm doesn't sound like much, but it makes a big difference.
Your list sounds rock solid but remember, whatever you end up deciding on must be documented on this forum with pictures.
I may well go the 300mm route, being a home cook I'm not too confident with longer knives but can see the benefits of going longer in this knife and I think the longer yanagi look so beautiful. I'll ensure I post a picture when I purchase.