I don't know if this
review is any help? If you interpolate the last lines comparing the topmodels (with hyperelliptical needles) for simples nude elliptical needles, it is implied that the Clearaudio has a better engine, better body. I think the Clearaudio is made with a lot more attention to detail, and this shows up in channel separation and -balance which are significantly better.
If the price is the same I would take the Clearaudio instantly. You can say that is has an interchangable/upgradable needle, but that is almost the same price as a complete new cartridge which invalidates the entire argument. ($236 vs $236 while the CA is $400)
I was just reading on a German site (comparing prices and consumer opinions) and found one buyer who upgraded exactly from the Blue to the Performer V2. So someone who knew the Blue intimately. And he was very happy with the upgrade. He discribed it as: "Brilliant highs, fullbodied welldifined bass, very good differentiation of details, while maintaining a coherent soundstage and smooth sound. Great! A minor flaw is the slight tendency for sibilance mainly on higher female voices. But I can live with that."[FYI: he built it in himself, being a novice with big hands, so it might be slightly off]. The craftsmanship of the ebony body gave him a big smile because it feels and looks very expensive.
Another user upgraded from the Red, and he stated the upgrade was 'unbelievable'. So I think this answers your question pretty much.