My call is D.lindleyi. I've seen jekensii in flower at a friend's place and while the flowers are the same size as D.lindleyi, there were only two or so per inflorescence. There is a "large form" of D.lindleyi...oh, check out my posts on this page:
dendrobium lindleyi?
I think that's about the limit of my knowledge of this species. Measure the flowers to see if it may be [I]var majus[I] and that's about it. The more common orchid is, in my experience, the most likely. But you never know.
Cheers,
Aus.