I normally print 11x14 or 16x20 and have no problems focusing.
I use a Beseler 45VXL enlarger with the Dichro 45S light source and a Peak grain focuser.
Lately, I have been printing 8x10's from 4x5 TMAX 100 negatives. If I open the lens up to focus, I sear a hole from my retina to the back of my skull. The grain is so fine and the light is so bright that I rarely feel like I nailed the focus. If I stop the lens down a bit to see more comfortably, then the grain seems layered or imprecise and that does not work very well.
What do others do when trying to focus with a bright light source? Just occurred to me that I have an ND filter that will fit over my enlarging lens. does anyone do that?