I'm unconvinced Westbrook can make a solid #2 back this season simply because he won't see enough touches. I was a Westbrook owner last season that was forced to start Westbrook for several weeks. I knew that by starting him I was guaranteed a bad FF score unless he scored a touchdown. Luckily he managed to consistently put up TDs with like 10 touches per game (freaking crazy).
This year his touches should increase, but not as much as people think. If anyone remembers last season, when Duce Staley went down, Buckhalter became the starter and Westbrook kept a similar, limited role but with more touches. I think that is the type of role he will play this year, a limited role with less than 20 touches per game. Not exactly RB#2 material for fantasy.
I think Westbrook is extremely talented and has a strong chance of matching his TD totals of last season. But I don't think he will have enough touches/yardage to be a player you want to start week in and week out. Unless of course you manage to get awesome talent at the other positions because you did draft Westbrook as your #2.