I don't have specific comments on the models you're looking at, bud I did shop Klipsch as they were changing. I demo'd RB-35's and an RC-25, but I was really looking for RB-25's. I wound up going with Ref IV, RB-61's & an RC-52.
Klipsch says that the horns in the Ref IV are "more refined", and I guess that's true. Another way to put it, however, would be to say that they lost some of the "liveness".
I see little difference in the RC-25 I demo'd & it's replacement, my RC-52. All in all, I'm pleased with the change between the RB-25 & the RB-61. For a few dollars more I got a speaker that wasn't too much bigger in front area, but was deeper, with more volume & weight, and went 10hz lower.