Dave, no highland survived my conditions so far. I am in constant 30+C (90+F) nearly year round. Surprising, the muluensis x lowii is producing good sized leaves at my balcony where I grow the rest of the Neps. The leaves are turning to face the light so I guess it can take more light.
N. sibuyanensis is threatening to croak on me already. The leaves produced are not unfurling.