Is there usually a dramatic difference between $5k and $10k cartridges ?

Yes, the cost.

They will inevitably have different materials and design choices that ensure a different sound. Which one you like better may not be correlated to the higher price. If you’re talking about upgrading within one brand line then it’s a safer bet that the higher cost one might sound “better”, but even that’s not a 100% guarantee.

But most 5k and 10k carts will in fact sound pretty great overall; it will be hard to find a dud. At the very top tier prices the manufacturer can take extra special care selecting only the very best coils / motors - I think that’s what Koetsu did with the Blue Lace model, and it does sound better than other stone models to me.

It costs at least $10,000 retail to make a cartridge. Just as it costs at least $200,000 for an automobile. Anything less expensive is merely compromise for the poor.

Just like most things in HEA, at a certain point doubling the price will likely yield a 10% improvement in sound, but if you can afford it, why not?

At that level there is generally not a dramatic diffeence between any 2 components  You're chasing the last few percent.  that is not a bad thing.

Now people will get very excited when they make progress.  Lets do the math with some made up numbers to illustrate:  you're at 97%.  You find a component that moves you to 98%.  It is only 1% improvement but it got you 33% of the remaining and it is a big deal to you. 

Jerry