I have been trying to do a few more things.
Build a song is a less common time signature. It looks like the time signature for the song is taken from the filter one selects for the patterns. This means you are pretty much stuck with 3/4 or 4/4, there are 6/4 and 6/8 pattern but they are just "endings"
So I need to build my own patterns. It appears this has to be done in the DAW, saving the pattern as a standard MIDI file. There are 22 options so I think I need to make a drum map pronto. This sounds more than OTS but consider it includes individual strings, top strums and the like, all of which are extra to OTS's articulation, all in all iits less intuative and a lot more messing about than the OTS method. I am hoping that 5/4 patterns, when added to the library will alow the construction of a 5/4 song, watch this space for an answer. The song builder does seem to be allergic to meter changes, I could not mix 4/4 and 3/4, maybe I am missing something.
Songs can be exported as MIDI, I suspose the intention is the generated guitar part can be used with another VSTi. Of course it can but with limitations. The articulation information is not (cannot be) included so all your mute strums will sound as sustains. I tried a track with Real Strat (old version without the song builder) and it sounded pretty rough!
You can export the song in a propriatory format that could be used by the other Realguitars as long as you have upgraded to the latest version.
This leads on to another consideration, It dosen't seem you can drag the song into a MIDI track in Sonar and play back it back exactly as one would using the internal sequencer. So one has to keep everything in RealRick song sequencer or record it as Audio. Freezing does not work, one has to record the output of the VSTi, This is fine in platinum but I am not sure about earlier versions of Sonar.