Personally I use a 15px feather, it just looks better to me, but if that's what you like then that's cool too
To me,it seems to be overblended, fades too much in the BG, works better for bigger renders. Good Job.
This is the same method I use sometimes, it's a quick way to blend. I didn't know about the white and black brushing to blend and unblend the render.
the biggest problem in signs is the picture don“t "face" on it.. those people should seen this tutorial