Yay, that is the spirit! Well done Partyboy – perhaps your all knowing wisdom and magical web skills will point me in the right direction to the cycling website that tells me which headset I should buy for tapered headtubes (given there seems to be numerous different standards out there which cater for intergrated, semi-intergrated etc.).
But hey, guess what, phoning Orange is exactly what I did just prior to posting this thread (being an obvious retard for not instinctvely understanding something new to the industry). From their technical dept:
Orange: "Why don't you just order it from us with a headset installed"
Me "Well, I've already ordered it, and I'm not the biggest fan of Cane Creek headsets. Is there any chance of telling me which format I should buy from another manufacturer?"
Orange: "You could get your LBS to phone and ask us for a Hope one installing – the different sizes and formats is quite confusing and it'd be a pain to get the wrong one".
Me "You're not kidding, I'll look into that, and see if they're not too late. Is it possible you can tell me the correct one anyway?"
Orange "Ok, thanks for calling" Click.
To all the other helpful people, my forks are a standard 1 1/8" steerer. ZST25 is just Cane Creeks model name for the one fitted to the Orange, so doesn't tell me anything about the measurements I should buy – I've checked the CC website and it doesn't give anything away there either.