I had a SOTA sapphire and upgraded to a Cosmos so I cannot give you an exact comparison.
I enjoyed my stock (series I) sapphire immensely. Decided to treat myself and bought a Cosmos and had SOTA make it a series IV. The Cosmos gives music a deeper blacker
background to spring from. The music opens up a little more and listening is more enjoyable. It is a "definite" improvement over the sapphire. Having said that, I could still live with a sapphire. I suspect that upgrading it with the vacuum would make the gap smaller between a sapphire and Cosmos.
Having owned both non-vac and vac. I highly recommend going the vacuum route.
Have Fun!
I enjoyed my stock (series I) sapphire immensely. Decided to treat myself and bought a Cosmos and had SOTA make it a series IV. The Cosmos gives music a deeper blacker
background to spring from. The music opens up a little more and listening is more enjoyable. It is a "definite" improvement over the sapphire. Having said that, I could still live with a sapphire. I suspect that upgrading it with the vacuum would make the gap smaller between a sapphire and Cosmos.
Having owned both non-vac and vac. I highly recommend going the vacuum route.
Have Fun!