Looking for the best moving coil cart that is around $5K used

I agree with mmakshak! A well-setup Sondek is indeed hard to beat! I have one myself, along with two Ariston RD's (the Linn's cousins). And I have kept them all in use, preferring them to today's pricier TT's! Get the best TT you can afford - even if it means skimping on the cartridge.

I don't want to write a treatise on analog v. digital. I have a Nantise/Lenco turntable with an Ikeda Kai cartridge, a 407 long tonearm, a Star Sound Platter Ground, and a H-Cat X12 current phono stage for analog.
  For digital I have a Surface touch screen control unit, and for digital, an AMS music server from Archiving Vinyl, an Avarii dac with JFET amplification. My digital sources are all double DSD initially on SACD.
  There are many differences. For one their sound stages differ. Digital is what the mikes receive and analog is what the recording engineer seeks and is more of what an audience hears. Second, there is more detail in digital, of instrument noises such as more harmonic as well as fingers sliding on strings. Finally, digital has highly defined locations of the sound stage and better high end.
  But analog is smoother, has more music hall or studio decay, and has more familiar instrument sounds with brass and drums not accurately reproduced.
  These observations come fro about ten instances where I have both analog and digital versions of recordings.
  There is no question that digital captures more detail and precise location of musicians and signers and that some of this is not music but it contributes to  realism.
  Vinyl, however, gives more hall decay and sounds familiar.

I read recently that the most important part of a phonograph system is the turntable, followed by the tonearm, folled lastly by the cart. It doesn't make any sense putting a $5K cart on a $400 TT/Arm. I would recommend selling your two tt setups and buying one new one of the best quality TT  and Arm possible and run it with the cart you have now.

handymann

At $5000 used, you have many wonderful phono cartridge options.  Nothing is perfect in high end, so chose something which best suits your preferences.  Try a used stone body Koetsu for sheer tonal character or perhaps VDH Colibri African Blackwood Mk.2 series if you cherish speed and dynamics.  See if you can borrow something first, if possible. 

On Audioasylum there's a NIB Kondo IOm cartridge listed for $5500. Went new for well over 10k.