I moved from an RT to the GS and have never looked back. The ergos of the GS fit me so much better, and I am only 5'10". And the GS is so much more nimble. And no removing heaps of plastic to service the bike properly. You just can't go wrong with the GS.
But. You really do need to ride both bikes, giving them both a fair shake. You can't go wrong with either, one is going to speak louder to you than the other and you will know which one that is.
When you have had the RT for a couple of years and you are still yearning for that GS you had always wished you had purchased, you can trade the RT in at that time.