I took @Gsuberland's comments to heart, and tried encoding Aerials at different bitrates. Upon careful listening, I could pick out the 128kbps version. CBR 192, ABR 160, ABR 192, and CBR 320 sound exactly the same as the FLAC to me. Casually, I can only tell whether it is 56kbps and below, or "good enough". 64-128 CBR sound good enough to me. That said, I always use ABR 192 to encode. I wrote a simple PHP script to do the double-blind encoding, just generates X random numbers in an array, writes that array to a file, and then encodes using the value at each array index as the filename. Random enough for me.