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

If they sound "worlds apart" then is it possible that none of them sounds right ? Or it is more like fine musical instruments that are different but both sound right ?

Yes, that is correct - cartridges are not a great pursuit for those seeking an "ultimate truth" (whatever that is). I prefer to think of them as performance artists :) 

That's a good approach, I think, because any other one will drive you crazy.

I am also on the hunt for a new, better cartridge, and I expect to pay 2x or 3x more than the cost of my current cart.  With that being said, I will only buy a cart that provides significant improvement. 

@carlsbad2 

When you state "It is only 1% improvement but it got you 33% of the remaining and it is a big deal to you.", I can agree that the logic (math) is correct, but I find the premise is wrong.  

When a system improves from 97% to 98% , in your example, it is assumed that the SQ improvement will be audible and valuable .  As many have noted in other strings, slight variations/improvements are hard to notice/remember even after a few days of listening.  I expect most AGs will not spend an extra $5K (double) for a 1% improvement.  

This is not meant to be argumentative, just objective.  There are always new-folks looking for reliable, realistic insight and advice...

Anyone ever buy demo/used cartridges? Thoughts? Experiences?

Anyone ever buy demo/used cartridges? Thoughts? Experiences?

I've bought plenty both new and used. Best is buying used from hobbyist audiophiles with stellar feedback who cleans their gear compusively (i.e. check the cart picks for a "dust beard", look for a clean stylus pic). Many of us also have large cartidge rotations, so no one cart gets too many hours. Never had any issues with cartridges bought selectively this way. Dealer demos can be OK-ish, but are usually not kept nearly as clean as the best hobbyists. And if you're buying from a gear flipper whose expertise caps out at fuzzy iPhone pics, good luck. 

But if the seller is at all honest, and their feedback is to be trusted, they should be able to accurately describe the cartridge's condition, age, and performance. I've actually had a much higher rate of various issues with used (active) electronic components.