Unless the RV5 has been fitted with single coil pickups, which would be an after-purchase change or through a request to Sadowsky, the two basses would actually sound fairly similar in active mode with the pan centered. Either is a quite modern sounding bass with the hum-cancelling pickups.
They share the same bridge PU. The only difference is going to be the offset coils of the P design, which do give you a very true old-school P-bass kind of tone when soloed in passive mode. You are also likely to a get a little "thicker" sound with the split P.
I guess it is fair to say the P is a little more diverse. Although, the Sadowsky hum-cancelling J has pretty much defined the Sadowsky sound. Which, in case you haven't heard, is quite highly thought of by many.
