Jk is my favorite as well, but I have a vested interest.
fz: As you know, the JK is a little larger in the throat of the grip than the standard riser. Normally, it also involves reducing the heel by 3/8 inch, but Larry will take it down to 1/2 inch. I have two like that and another on order. Pretty hard to beat.
Buckster, I tried out the 14-inch RC at K-Zoo a week or so ago. Very nice. Didn't think I'd like the finger grips and thumb rest, but I did, plus the little extra wood in the palm of the hand really felt nice. A little lower heel than the standard riser, I think. If you like a recurve grip, I think you'll like this one. A little beefier than their standard riser.
I've also owned the 16-inch standard riser. That was very nice also, but I like small risers so the 14-inch works a little better for me. Haven't had an opportunity to try the replaceable grip risers yet.