The ideal girth for myself is a spot-on 6 inches. My birth date is 8/6/86... would be awesome if I could also say my dick was 8x6 instead of 8x5.75. XD
In another guy, I'd say 6.25-6.5 is an ideal girth. I say that only because I'm unable to take the 7 inch girth of my toy. :s