I could be wrong... But even doubling it over your not going to add it all up like that... The weakest link is still the weak link... Once you get 275 lbs of weight(using your math of 50% in the knots) on that knot It's breaking... When 550 breaks, you get a little warning... You will hear the 7 strands break one by one when you move... Then the last few and the outer jacket will all snap almost simultaneously...

But the first rule in hanging is never hang higher than your willing to fall... So hang your own hang... Put some padding on the floor and sleep comfortable in your own math...