A typical glass and curtain wall assembly rates around STC 32. That lets loud speech through, so it is often worth upgrading between bedrooms, offices and meeting rooms.
Most effective upgrade
Use laminated glass, double glazing with a wide air gap, or an inner secondary pane.
Acoustic panels on the surface add only 1–3 STC points. They are for the sound inside the room. See STC vs NRC and flanking paths.