From I remember it used to be on the r3mix site but that's since been taken over by a domain squatter.

There's a big comparison page here though. The results for AudioCatalyst 1.5 and 2.0 (non VBR) are missing for some reason but 2.0 VBR is still there.

General consensus is that 1.5 sucked and 2.x was a lot better but still had a couple of minor issues.