Just in case anyone is interested, it now seems to be fixed with both GPU and CPU maxing out at 85oC under full load.
Tried lots of things; another re-paste, massive under-clock to GPU, fans to 150% with it always still hitting 92oC after a couple of minutes, then the other day it just started to work normally again after trying nothing for a few days. so all a bit odd.
I do however suspect there is an issue with the GPU cooling fan as there is a lot more air blowing out that side of the laptop, hopefully it wont happen again but if it does then will probably just replace the fans.