I have a Ti Crown Jewel and an RSL, and there really is no comparison. Don't get me wrong, the TJC is a beautiful bike, but it's more like a Vamoots than an RSL. Super smooth ride, handles beautifully, great build quality, etc. I haven't ridden one, but I would suspect that the closer comparison to the RSL in the IF line-up would be the new IF Ti Factory Lightweight.
Imo, the RSL represents a whole 'nother level of performance in ti bikes. If you want the supercharged snap of a Tour-level carbon bike with the smooth ride of ti, get the RSL. Of course, if the price is right, it wouldn't stop me from getting the TCJ as well... ;-)
P.S. I must've been typing at the same time as ggw, and I agree with him 100%. It's a bit of apples and oranges—both are sweet. The RSL is designed to be a pure-bred race bike, which isn't for everyone, but that's why there is a spectrum of choices (no pun intended).