i know it´s a beginner question…but somehow i have a knot in my brain 
f.e at a resolution of 800x600 i use -3/1 for higher quality.
now i want to render a picture with 2800x2100… for that you can calculate the irradiance map with a lower resolution, store it and render a bigger image. but what min/max rates are the best when i want to calculate and render the image in 2800x2100 ? -5/-2 ? or even more ? -6/-3… i know, i know…shame on me…but i´m so f!"§!$ tired at the moment 