ID help, please

I can't figure out if this is a Sharp-shinned Hawk or a Cooper's Hawk. Any pointers on how to differentiate between these two as it pertains to this photo would be appreciated.
Taken in late fall in the mid-Willamette Valley (Oregon).

I would go with Cooper's based on the tail shape. Here on the folded tail you can see that the outer tail feathers (on the bottom of the folded tail) are shorter than the central ones, giving the bird a rounded tail. On Sharp-shinned the tail feathers are all roughly the same length. If you have a different head angle, that could help confirm--Cooper's Hawk has a nape (back of neck) that is paler than the cap, while on Sharp-shinned the dark nape connects the dark cap and back uniformly.

First instinct was adult cooper's hawk

see this link:
http://www.naturephotographers.net/imagecritique/bbs.cgi?a=vm&mr=76294&CGISESSID=69a22b6aef475d6a3b0d0432fa1aee83&u=25009

and this one:

http://www.naturephotographers.net/imagecritique/ic.cgi?a=vp&pr=214265&CGISESSID=69a22b6aef475d6a3b0d0432fa1aee83&u=25225