With regards to burbidgeae... From what I read, its a well known fact tat highland species seediings greatly benefit from higher temps in early stages of its life. Have you found that adults grow better at intermediate as well? I understand your argument...another bit of evidence to this matter is from Joel's website:
source: http://www.nepenthesaroundthehouse.com/nburbid.htmIt seems that this species doesn't tolerate as low of temperatures as other highlanders. I would venture to guess that it does real well in slightly warmer conditions as an intermediate. I've heard from some other growers having success growing N. burbidgeae in areas of Florida as a lowlander but I don't know if that is entirely true.
For sure, higher temps lead to increased growth, faster metabolism etc. But analogous to VFTs skipping dormancy, how long can a N. burbidgeae hold out in intermediate conditions. If what you say is true with regards to the median of the population lying with N. rajah in the highland range, that might provide the answer that: N. burbidgeae is tolerant for prolonged periods at intermediate "conditions", but requires highland "conditions" to persist long-term.