I got 2/6 right, the 4 wrong were 320kbps. Using the cheap-but-decent shp9500s and no dac, but quite good hearing. I'd chalk it up to having been listening to almost exclusively streamed 320kbps, it was interesting to note that the 4 I got wrong were because I discarded the more 'neutral' toned one which was actually lossless.

The 128kbps was of course very easy to pick out.

I'm of the opinion that 320 vs lossless is meaningless enough to not really bother, but I know for some tracks it was trivial for me to tell the different. Mostly it was the very complex/atmospheric tracks, Mind In A Box being a good example, where 320 lost a notable amount of quality. Probably others like Ne Obliviscaris as well.

The biggest problem with Spotify is that not all of their library is available at 320kbps.