I'm inclined to believe it's pure D. speciosum.
D. kingianum generally has broader lateral sepals (not present here) and the lateral sepals are more horizontally reflexed (they bend outwards, like the motion your arms make if you hold them first straight out in front of you and then move them outwards so you assume a "T" pose).
D. speciosum, by contrast, tends to have thinner, longer lateral sepals that stay on one plane and look sort of like a "U" or a lobster claw.
Dendrobium x delicatum actually kind of has a mixture of both where the lateral sepals are in a U-formation but they are definitely shorter, broader, and wider apart/slightly reflexed. I can't really see that here.
Also, another note... the lip of D. speciosum is more pointed/arrowhead-shaped (as seen in yours) while the lip of D. kingianum and D. x delicatum are much broader.
Wikipedia has a nice section on the different varieties of D. speciosum, by the way. They list an average range of flowers each type produces (but of course it's still highly variable, depending on factors like age, water level, etc.) I think it's worth checking out.