The dvars in question are these:
cg_fovcompmax 85
cg_gun_fovcomp_x -2
cg_gun_fovcomp_y 0
cg_gun_fovcomp_z 0
This allows you to change the way your viewmodel scales with your fov, i think this is a resource the developers used to make the animations look good when using high fov values but it also creates a distortion effect making the guns look longer.
The position of your viewmodel will scale from the default fov to (cg_fovcompmax) value.
I think this is a very cool feature that brings more customization to the game.
So i'll love to have this in bo2, i don't know if it is possible... what i know is that bo2 has the same viewmodel scaling as bo1, when you change fov 65 to 85 notice how the viewmodel moves back probably to -2 (same as bo1 default values) but sadly the dvars are not available in bo2.