If the decision tree doesn't answer you question let me know. I'm working on the 6.5 update and would certainly like to incorporate any feedback.
It really boils down to 1 question - Do you need Enhanced Linked Mode? It sounds like you don't right now but might in the future. The thing is, there's no way to merge or otherwise combine two different SSO Domains (at least not as of today). So, I wouldn't add the complexity of an external PSC if you don't need it today. So, with the limited information we have, I'd say stick with embedded PSC.
