I took the plunge and also got the GPO5 upgrade. While there are still some rough edges here and there (seems a bit rushed out), there are some impressive improvements for the prices.
Like others, the Intimate D piano is just something (worth the money by itself). So, here are two bits of work that highlight what GPO5 can do.
1) The intro to a piece called Why Me? (All GPO5 strings but took some blending and EQing, GPO choirs (boys and full), Kontakt VSL choir, and Ivy Audio - Clare -- which is free and really nice).
2) In salute to Ennio Mariccone (and my parents 50th). Gabriel's Oboe ala GPO5 Intimate D and Embertone Cello. Both tracks were played live (piano on keyboard) and cello on the EWI.
The strings are pretty good improvement and quite usable with a bit of fiddling. Again, for the budget well worth it.