YES, Matt you're correct, I made some maths and calcs and should be around 5.5 Kg at the lightes rideable wayDangerholm has got a modern HT Scale 29er down to 6.2 kilos. That's had shit loads of cash, expertise, custom components and time thrown at it. I'd not be surprised if it owes him €20000 (if it was a stand alone project). A rigid 26er you should be able to get well under 6 with the same sort of approach.
SebK's 4.5/.7/.8 kilo bike is an irrelevance. Unrideable in any sense of the word. I'm amazed he isn't dead based on some of his more questionable modifications. But then the bike never gets ridden, so maybe I'm not surprised.
So I will change the target