First of all, let's compare the switching options on both switches:
3 way: bridge, bridge + neck in parallel, neck
4-way: all of the above and bridge + neck in series
So the three identical positions on both switches also sound identical - there is no sound degradation due to the 4-way switch.
The bridge + neck in series has more output than the other positions and also more noise - this is why a RW/RP would be beneficial since the single coil noise adds up when both are in series. Personally I could not care less about the series linkage - I play about 70% on the bridge, 25% on the neck and only 5% on other positions, except with the strat where the 25% are split between the neck and the bridge + middle positions.
I have never had a direct comparison between an otherwise identical standard and RW/RP pickup but I can assure you a RW/RP pickup does not sound bad just because it's RW/RP.
Cheers Stephan