I travel IAH--SFO--IAH on CO about once a month. I just got onto CO Gold elite status. A few questions:

* Is there much difference in getting upgraded on this route as a Gold Elite versus a Silver Elite member?
* Are there any particular days of the week when this route might be more susceptible to an upgrade?
* How do you figure out whether to expend reward miles for an upgrade on this or any other route, when your're holding Gold status and might get upgraded anyway?