BOAC,
I think the only thing that rules out the "Northern Arc" is the lack of any reported radar returns that way consistent with a mystery 777, and also a lack of a wrecked 777 out that way, but then there's a lot of nothing in central Asia.
It could have avoided radar coverage on an early weekend morning, and be waiting to be found in a hole in the desert or mountains somewhere.
But if it impacted on land, you might expect to have heard from the ELT beacon?