This was a very good test. You, sir, picked a very good song for this test (in the sense that it’s very hard to tell the difference). It took me several listenings to pick out the correct one (which i did manage).
Now i want to point out a few things here.
First of all, you didn’t specify how the encoding was done and with which encoder. You see, 128 kbit MP3′s are typically ALWAYS encoded in Joint Stereo by most modern encoders, while 320 kbit MP3′s can often vary between normal …

Hey Guys… I think it is difficult to tell for someone listening through home speakers or car stereos… or even a pair of very good consumer grade headphones. But as a DJ… the difference is astronomical when you play it in a venue through a loud system. The difference is even more astonishing when you play through a system that is EQ’ed properly and has speakers and acoustics with a wide range of frequency responses.
I’ve made the mistake of playing a set with a couple of MP3s mixed into a …

I heard a difference between the mp3 and wave versions, except I hated the wave version! I found it to be -worse- than the mp3. It was [cold], its musical life had been [erased] somehow. I would certainly not create a master from -this- version for pressing. It does not produce the same harmonics as the mp3 versions I downloaded (yes, plural. Long story short, I ended up comparing 4 copies of the mp3 vs. 1 of the wav. file). I suggest something in the conditions was different when the …

Immediately chose the correct value!
The trick lies in listening to the reverb of the instruments and voices in the music.
In general this style of music is easy to compress, due to few high frequencies, and quality is very even, but there are plenty of songs that will give you artificial noise in the higher frequencies.
My recommendation to you would be to have all encoded in OGG.
The average songs don’t compress as well as this one did (did you compress in 128kbit avg, or variable bitrate, or did you encode it …

Matt here again. I took an mp3 listening test here a while ago. The shoot out was between an mp3 of 320kb/s vs. and mp3 of 128kb/s. A number of people commented that a test between a pure wav. file against a 320kb/s mp3 would be more useful.