What happens when I print a 0,6mm thick wall with a 0,4mm diameter nozzle?
I'd say you should experiment with Slic3r

it can manage extrusion in very sophisticated way

it can overextrude if you need a line wider than actual nozzle size
as same as it can underextrude if needed
it can even change extrusion continuously while extruding one line

here are simple examples






i use mattercontrol

take a look here - this is the same object the same layer and the same settings

please notice - this object has wall thicknes exactly 2 times nozzle diam

here is what i get with 


native MatterControl slicer engine which gives this slice

and Slic3r engine which gives this slice