cg_errordecay
This cvar controls how fast prediction errors decay off. High values can cause clipping errors which can be abused for seeing thru walls. I don't see any reason why someone should change this cvar at all. So this one could be cheat protected or capped at some range.

cg_fov
Players are able to see thru walls at the edges of the screen if fov is set above 150. At the moment fov is capped at 160 (higher values affect only to the gun model).

Screenshots are just examples. Both exploits can be used in any map.