I had trouble sharpening the GFK when I first got it. If I remember rightly, it has a really quite large/convex grind on the edge?
I didn't bother sharpening it until I got my lansky, then went to town with the extra coarse hone, grinding the edge flat @ 25 degrees. The thickness of the steel and the way the relief + false edge are ground mean it would take a lot of grinding to get it more acute.
Currently I use the hones @ 25 down to fine, then micro-bevel (I think?) @ 30 with the ultrafine (1000 grit). I don't really know why I micro-bevel. Anyway, it gets it hair-popping sharp, which I think is good enough for most people.
Yay first post.