I think the 1580psi (Table 2A?) is the tabulated bearing strength of a species. In this case your still designing the brace, so I would use the Fcparallel value of 700 or 325, if the member will be 5x5 or greater. Larger members have higher tabulated values b/c imperfections won't effect the overall perfomance as drastically as smaller members.
As for braces, I agree with the pairs, so that there is always one in compression. And I think they're function is to resist lateral loads. ie Apply one wind load case, determine the compressive force, then check other load cases. I definitely wouldn't view a beam as two because a brace was connected to it. I hope this is helpful, good luck, Joe
PS Once you select the member, then you need to check the bearing str at the beam and the column, typically at some angle, see section 3.10 of NDS.