Conger probably holds him below ten - Conger wouldn't have won because his a socon, but he definitely was the more talented candidate between him and Wehby, and if he had won the primary he would've given Merkley at least a scare.
Considering the wave, Smith definitely could've beaten Merkley.
There was no wave in Oregon. Or really anywhere on the West Coast.
That can be said at a federal level, but statewide, Gov. Kitzhaber didn't even break 50% against a very low-funded, terribly conservative Republican candidate.
Merkley would have beaten Conger by a similar margin as he beat Wehby by I think. Wehby got hit by the sexual harassment scandal at the same time as when she was getting nominated while Jason Conger is a social conservative to the right of Wehby. Both were very flawed candidates.
As for Smith, he would definitely have made Merkley sweat. Merkley is weaker than Wyden; barely beating Smith in the '08 wave, but Smith is a little too conservative for Oregon and I think voters would have narrowly rejected Smith at the polls again against Merkley.