Mark Pred said:
Interesting, as I'd say this 'gap' you refer to, is very small, even non existent. Performance wise, the two cars are quite close, much closer than you'd think. Each to their own, but for 95% of the time you drive these cars, they're almost identical, is it worth ten grand for another 5% and a badge, not so sure it is

Roadster? Get a Boxster, end of. Never get why people buy an RS Roadster when there's the Porsche out there for similar money.
This is why the OP needs to just go and test drive. It's not a shock really that TTS owners generally don't perceive much difference between the S/RS and TTRS owners think there's a large difference.
That 5% difference is probably right, is you don't care for power/noise as it's just a few trivial bits or interior trim really and a slightly different bumper. I think the carbon option and start button being on the wheel is the only premium the RS has. But for engine, it's 25%. And for me, that was actually all that mattered, so I'd weight it at that end of the scale; as said - each to their own.
On the road, the extra power is certainly noticed, but 'on the road' the 5% valid there too - but then that goes both ways, a base FWD TT would be on the heels of the S, cars are so capable nowadays!
The problem with the Porsche (and I love them) is that if you want the RS for the motor, and we've established that is the only real justification over the TTS, then the Boxster doesn't cut it.