Hi there Mig25,
The Single Six is one of my favourite revolvers, and the very first one I had ever bought. I started out with a 6 1/2" Single six with adjustable sights, and found it very accurate. However, I fell in love with an older series 5 1/2" model with cowboy sights, and sold the 6 1/2" piece to buy the cowboy.
Believe it or not, I found the 5 1/2" cowboy model more accurate! At 25 yards, I can easily put a 1" group on paper with just the fixed sights... I have owned a few of the 4 1/2" Single six, but these I have not found to be anywhere near in accuracy to my 5 1/2" piece.
I've recently acquired a 9" Herbert Schmidt copy of a Single Six, and am in the process of putting target sights on it. I'll let you know how that turns out. However, for a "Hunting piece" I believe that the 9" piece will have a definite advantage with its sight radius.
Hope that helps,
w.w.w.