HD SR master and HD Cam screeners

I am wrapping up my first film and have some technical questions. We are doing out layback on a HD SR mater and will be making HD Cam screeners. I am being advised to wait to do our conversion till we know where we ar egoing to premiere. Is that ill advise? How do I get the best quality possible on the HD Cam screeners if we wait to do the conversion? Also, we shot on SD. Is it better to have a HD SR master in stead of a D5? Thanks!