I think the texture needs enough open spaces, no solid green mass of needles (nice as it may be). I make my own textures (gathering branches and photographing them in front of a white board), so have to take care about that. A PF to lessen opacity would work for distance, but not for close up.
I was also thinking about TIF+alpha channel (which was my principal way of saving) and PNG files; the latter is smaller and looks like it's working just as good. Interesting to see it has no alpha channel, but in TG you still have to check 'use alpha channel' or it won't work.
Also; when importing a TIF+alpha you have to load it twice (for color and alpha); cheaper is to have a greyscale tif for the opacity, and a TIF without alpha for color.
So, what do you guys use, and think about this?