I REALLY like the work you put into this. Keeping them the same file size, same sample, and volume equalized must have taken some work. Well done!
I only went through the first one. Based on my quick listening, I did get the answers correct, but I always love listening to these things, because they show how subtle of a difference all the Flac vs mp3 is, especially when you consider the 320 bit rate. I saw some people's comments about listening to brightness or presentation to pick out the differences. I believe somewhere a study was done and people with ibuds liked 128 the best. I think this leaves out some details in a song, and makes it sound more forward.
Anyway, the way I can easily pick out the differences are when I hear any kind of moraca or a drum brush (like at the 0:10 mark). Also something to listen for is the subtle decay of guitars (like the decay in the 0:04 - 0:06). The subtle decay from a brush or the individual beads hitting are lost in 128, and 128 can easily be spotted doing this. 320 and Flac is a little more difficult.