ok not sure if this data is of much use as the cage hasn't really cooled down much since his heat bulb went out. He was looking pretty unsettled however, so I didn't want to bother him for much longer.
Branch opposite side of cage at 5inch: 72.14 (measured after other readings)
5 inch: 80.6
10inch(ish): 74.48
so yeah, I've tried to be accurate but take these two data sets with a pinch of salt as I'm definitely no scientist. I'm glad I tried this though as it was eye opening. Jungle dawn + heat lamp + UVB bulb must = a pretty hot top of the cage. Time to be keeping an close eye on more than just his main basking spot.