I know this is an old thread - but I'll add my two bits -
The CF loaded filament definitely eats a brass nozzle as you watch
The "Hardened" nozzles sold as "plated", "coated" etc, are only a little slower to go
The actual tool steel nozzles fare better but still wear
The Ruby nozzles - you will finish your part with the same diameter you started - I've given up on any other nozzle for filled materials.
I spent a lot of time checking nozzles pre/post printing using a machinist's microscope - measuring to .001 mm and it became really obvious that you need something as hard as ruby or you will chase lots of odd things along the way - they don't even stay round...
In the course of your part, you probably went from at size to something larger as you printed - even if you over extrude a little at the bottom, by the time you get to the top, you will be under extruding (at least on tall parts) That plus the temp/enclosure/conditions pieces can add up to some really odd experiences.
I had one large part (pre ruby nozzles) where I had to keep manually "tuning" the extrusion rate up a percent at a time as the nozzle wore - it was a very long 26 hours....