For me, it was a no-brainer: I'm using it live, and so I really want a 5 octave keyboard with splits and layers. Of course, there are many other things that the '08 can do that the 6 cannot. I think the presets are better on the newer instruments though, and there are a lot more of them. As you can see in Starsky Carr's videos, the layer feature alone can make the '08 sound better for many sounds. When watching his videos, I get the sense that the 6 can sound marginally better than the '08 on simple sounds. (I also had this impression when I briefly played the 6 and OB6 in person.) How much better is pretty subjective: Is it 5% better? To me, it's probably not 10% better. If you read through The Prophet '08 Among Prophets thread, you will read about the advantages of using Sacred Synthesis' method of using two synthesizers panned to separate sides at the mixer. To me, this is not merely a marginal difference. How much better does it sound? Again, it's subjective, but I think it is probably more like 25% better. The current cost of such a setup is around $2,300, and it sounds considerably better than either of the other instruments alone. Of course, one could utilize a similar approach with the 6 or OB6, but at well over twice the cost... and you still can't do splits and layers.