Several unclear items in this thread.
It's not advisable to use the term "1Dx" as a referece to various 1D models, like the 1D, the 1D Mark IIn etc, since there's also a mode actually named 1DX.
There is no such thing as a flash called 680EXRT. I presume the 600 EX-RT is the one referenced.
There is no such thing as "single point metering". There's spot metering (for light) and sigle point focusing (for distance).

Ambient light metering pattern (spot, partial, average or evaluative) is non-related to flash metering (evaluative, average or spot (when using FEL)). Data from evaluative flash meteirng is augmented by lens distance data, if such data is available and the flash is aimed straight ahead.
Evaluative flash metering is biased towards the active focus point, prvied One Shot AF focusing is used.