I've had my RS-IIIb's since 1989 and they won't be leaving any time soon. I think it's a very good speaker, neutral sounding (i.e. not leaning towards warm or analytical), images well, with taut, fast bass that is only missing the lowest 1 to 1.5 octaves. Best served by an amp with some cajones.
And yes, it is RS-IIIb. The RS3 is an altogether different speaker produced in the '90's after Harman bought out Infinity, and of inferior design (IMO) to the vintage models.