Thanks, Walt. I'm guessing you have Advanced, if the upgrade is that much? I just have the standard version and can get the upgrade through audiodeluxe.com for $84.99.
However, I just installed the trial and the specific feature I was wondering about, RX 4 Connect, which is supposed to seamlessly integrate the standalone version with the DAW of your choice, is actually more cumbersome than having it set up as a WaveEditor for SONAR in the registry.
Oh, well. That, coupled with the fact that, like you, I'm not seeing anything new that seems like a "must have", I'm probably going to just stick with RX 3.