Hi,
we will also install the RC2N version. So only the increased number of mushroom head fittings. Our general contractor charged quite a bit for that: it was about €140 for a normal window sash and about €180 for a floor-to-ceiling sash (=terrace door).
When I searched on various vendor websites online, the price difference for otherwise identical windows was usually more in the range of €40-80. But that's just the fate when you build with a general contractor...
Best regards,
Andreas