I have a Cosmos MK6, its a fine table. The mag lev bearing is top notch. The combination of it and the Total Eclipse motor/controller results in a noise floor floor that is way down there, and the focus of instruments along with timing is top shelf. I don't know which version of the Cosmos you have, but the IV is supposed to have the same vacuum system as the current one.
I don't think you can go wrong upgrading your Sota. Cartridges come and go, but the improvements you are making to the Cosmos will outlast what you spend on it versus what you spend on the cartridge.
I don't think you can go wrong upgrading your Sota. Cartridges come and go, but the improvements you are making to the Cosmos will outlast what you spend on it versus what you spend on the cartridge.