650PH predictions make no sense because of all these reasons and are based on "well, if it keeps going on forever like it has for just the last two months then this is where we'll be" and not on all the things you are bringing up.
FWIW, I end up with very similar numbers when calculating the "end game", using todays BTC value and estimating costs based on HF's chip efficiency and estimated production costs:
The big unknown is how fast we will get there, it will probably take longer than a year, but I have no doubt we will get there if todays BTC value holds.