Ok so here's where I've got with this.

I went through the motions with a Mamiya 7ii but kept being beaten on price via ebay by sniping software, in the end this appears to be a good thing. I've now got my sights of a Technorama 6x12.
I went to an exhibition in London and saw Luc Delahaye's '132nd' which appears shot in 6x12 medium format. The damn print is 18ft wide. That's where I want to be.

So whilst I'm waiting for one to drop into my lap I've purchased a H1 body and a couple of extra film backs.

Those Technorama's look elegant, wondered about the Horseman 612 but it doesn't appeal for some reason.