Well the RSX is pretty much an ion firing chamber inside of a new body with modern fixtures. So If you like the smooth shot of your ion you'll really like the RSX.
I'd get one in your hands before you buy one outright. You may or may not like how it sits in your hands, which to me is a huge factor when choosing a new marker imo. I haven't gripped an RSX yet but I'm anxious to try one out. I always loved the ion platform and the RSX is like the highend version that never was.