That question depends a lot on your material. Is it: green or dry? hard or soft? end grain or long?
I'm sure you know, but secondary bevels can be great. They quicken your sharpening, add strength to the edge, and allow one to more easily change the bevel.
My low angle block plane is about 23 deg + 2 deg secondary bevel = 25 deg, and my slick is sharpened the same. My framing chisels are around 30 deg.
If you want good scientific information on sharpening, I suggest you purchase Ron Hock's book, "The Perfect Edge."
http://www.hocktools.com/perfectedge.htm
