My guess based on the bud near it and the inflorescence would be 8-9cm. Which is quite nice considering the shape of the flower. It could be bigger, though.
As to greenhouse etiquette. If you were in in my greenhouse fondling my flowers, I'd whack you in the head.

Or at a minimum bark really loud... So, you were correct in not wanting to touch it. I think that is more a function of me not knowing your skill and coordination level. Clumsy customers have broken or bruised a lot of my nicest flowers. If I knew someone was an accomplished grower or orchid judge, I suppose I would be not be as concerned, but I still think it would be nice to ask before touching.
It is equally nice to ask before photographing. I'm not a big time breeder, but there are a few plants in my collection I wouldn't want pictures of floating around. Why? Well, if they are really nice I want copyright control over them, and wouldn't want my plant used to sell somebody elses. So I might veto for that reason. Or, a plant might not be up to my standards and I wouldn't want that image associated with my name. Or any number of reasons.
Oh, and no smoking... :evil: