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

Exactly. Unlike cables, that in my view should be one step ahead of the active components or you won't hear what your system is capable of.

Surely whichever component (including cables) is the least transparent is the rate-limiting factor? And since improving on any bottleneck component makes everything downstream from it sound better, removing bottlenecks closest to the source have the greatest potential gains? That's what baffles me about "rules" like the "10% rule" quoted above.

@audio-b-dog 

Great news then that great pot is cheap... hmmm, the girlfriend could be problematic. 

I remember the Sears Silverton Suitcase Record player... circa late 1960's?

@dogberry Of course you are right. My 10% statement was just meant as a general guideline for someone new to the hobby.

For a person trying to thoughtfully put a system together, getting a decent cartridge that is a good match with your system (or the one you want to buy) can be tricky. Typically that knowledge comes later in the journey. My best advice for a serious
beginner is to work with a trusted dealer.

Note: 10% would be near the top end. There a plenty of great sounding carts that cost significantly less than that. Two of my favorites are my Nagaoka MP 110 and  Grado Gold3. Both of those carts are a hoot and will sound great in any system!