Ditto that. The runs out in OR are a lot less manky than here in CO but that being said there are a lot bigger features that may give you chance for face time with the river bottom... and a year round season increases your chances of a face shot too... I paddled with my WRSI without the chin bar for most of a year out there and didn't feel too exposed. When I wanted to start stepping it up though, into more solid Class V runs, I bought a SR fullface and never looked back. the fullface gives me a ton of confidence and has no real drawbacks except drinking/eating.
If you're going to only have one helmet, I would decide based on whether you are going to be paddling mostly harder stuff (pushing yourself) or just enjoying the limitless class IV that they have up there. Either way I think ear protection is a good thing to have in a creeking helmet.
hope that helps, have a blast! there is so much good paddling out there it is ridiculous. Half of the stuff never gets run because there are so many options!
"Paddle silently, boof loudly"