The answer to my own OP is no, it wasn't worth the wait - I bought a Shoei instead!
I know in the OP I said the Shoei didn't fit my head (large= comfortable, but too loose vs. medium= right fit but pressure points on temples and back of head), but it does (with a bit of fettling). Ran into a chap who unbeknown to me lives in the village and worked for Arai in a previous life servicing lids at race meetings. He said he still had the ware-with-all to adjust the interiors of helmets and showed me a toolbox with all manner of rollers, prodders, scrapers etc. So I ordered one here...
http://lidsdirect.co.uk/epages/eshop...onora_TC6-0003 for a fair price.
After five minutes in George's expert hands I had a perfectly fitting medium Hornet DS!
Verdict on the new lid...

A lot better than the Arai (bare in mind it was a first generation one) in almost every respect; lighter, quieter, better visor (with pinlock), got channels for my shades and IMHO looks more compact and neater. The only downside is I look like a paid up member of the Toon Army with the white/black striped colour scheme!?