Normally, I see crosses of this species. Also known as the "King of Paphs!" However, here is a link that perhaps can give you some scale. I'm not quite sure if this is a mature specimen; however, it perhaps could be close! Hope this helps:
The mature roth I have is approx. 24" leaf span. I would guess if you really grow it well it could up to 30+ ". They are certainly worth growing if you have some room. Pelepel is correct- King of Paphs!
I would certainly love to grow one, if my dendrobium spectabile wasn't being such a space hog and spiking like crazy! Ever read Orchid Fever by Eric Hansen? Pretty entertaining chapter about "The King" and I enjoyed the book overall.