Drilling the nozzle is the right answer for diameter problems. Why are you hesitant to do this?

1.60mm filament should feed fine anyway.

I've rummaged through the forums here a little to look into other examples of folks running polycarbonate or high-filler filaments, but would like to bring up my situation specifically to see if anyone has some words of wisdom.

Set-up:
-18V Filastruder in horizontal setup.
-Using a window fan under extruder as the mini fan broke (temporary)
-Using 1.75mm nozzle
-Ambient temperatures are a little over freezing currently as I have to run this outdoors

Material:
- Filled polycarbonate with a fine ceramic powder - I believe it's upwards of 40% by weight
- Documentation for material states Nozzle temp of 270-290C, and melt temperature of 265-280C

I've had success in running the material for the most part, although I've been trying to fine-tune the best temperature. I've tried several increments from 250C to 290C, with little change in my two problems.
1) Surface quality - I had one fluke run where I got a smooth surface, but 95% of the time I get a very rough surface (sandpaper-like)
2) Filament diameter - I am having trouble getting anything thicker than 1.60mm

I've been trying to avoid drilling the nozzle any larger, and am currently using the non-mesh filter one as I wanted to see if that would change any of my two problems above. Using the non-filtered one did provide a small boost in diameter.

Any suggestions? My next thoughts are:
1) Fix the fan to better direct the airflow problem
2) Try some lower extrusion temperatures
3) Return Filastruder to angled set-up (Not feasible with fan problem currently)
4) Drill nozzle wider as last resort
5) Find a heated room (No better solution with proper ventilation just yet)
6) Hope there's something I'm missing

The resulting material is also highly brittle - handling it in the low ambient temperature doesn't help. Once I fix the diameter problem, I'm hoping to remove the need to handle the material by using the filawinder that I haven't assembled yet...

Thank you in advance.