Pbarnette is right, if you want to change starpoints into Onepass miles, transfer to Amtrak first, then to CO. There is no 5000 bonus to transfer to Amtrak, however, and the transfers between Amtrak and CO are 1:1.

Be careful though, Amtrak limits how many points you can transfer into another program at 25000 per year unless you are an elite in their program. So at best, you can turn 25k starpoints into 25k Onepass miles per year.

For the record, I believe you get 12500 miles for 20000 starpoints if the relationship is 2:1.