I wonder why it is the 336 devices all seem to have twice the magnification as the "equivalent" entries on the 640 side (of the Zeus Pro Line) ??
Part of the reason they go with the higher magnification in the lower resolution units is to make them more usable. However, I completely agree with what I think is the spirit of your query. Wouldn't it be great to see some more powerful (higher magnification) 640 resolution scopes?
So what you are sort of left with is that buying the 640 resolution scopes gives you the option of the higher resolution, native magnification, wider FOV.