What kind of headers?

I'm looking to swap out the manifolds in my 2000 Chevy Silverado 1500 with shorty headers. Now, for the trucks engine size (4.8L V8), what would be the most appropiate primary tube diameter to purchase?...1 1/2", 1 5/8" or 1 3/4"? I'm also planning on installing a K&N cold air intake kit, which I would like for both headers and CAI to work in harmony.