How good does a TT have to be for a good cartridge

You can't go wrong upgrading the phono stage. The Gram isn't bad but can definately be improved upon. I suggest buying the best you can so you don't have to upgrade again later.

"My local dealer did a blind testing of carts on a very hi res system...the verdict/?...many couldn't distinguish between a 200 dollar cart vs 2k cart al things being equals...save your chips...other hi rollers will dispute this...but everybody wants to justify their purchases...even at the hands of clever marketing"

I've heard the same arguement for amps (so long as they're not clipping), cables, and DACs. To my ears, everything makes a difference. I may not agree with the hifi rags and some users as to the magnitude of the differences, but they definitely don't all sound the same IMO.

I've heard cartridges compared where all things were in fact equal, and heard a difference every time. This wasn't once or twice either.

Cartridges work by vibrations. Will every cartridge pick up every vibration exactly the same way? Different styli fit into grooves differently. Different cantilevers and their suspensions will allow those vibrations through differently.

This is the first time I've heard all cartridges sound the same though. I thought turntables and cartridges were immune to this nonsense, but I guess you learn something new everyday. Quite possibly the most absurd 'all x components sound the same' agruement I've ever heard.

How's this one - assuming correct placement and room acoustics, all speakers sound the same, except for low frequency extension.

I'm currently trying to answer this very question. Recently acquired a Dynavector XV-1s for my Scoutmaster Signature table (w/ JMW9 sig arm). I'm A/B this with the prior Sumiko Blackbird cart. One might think it should be a slam dunk with the XV-1s, but there's actually a number of traits about the Blackbird I favor over the XV-1s. This may be a result of better synergy with the table, the arm, the phono pre (EAR 834p deluxe) or all three. I actually have 2 JMW 9 sig armwands so that I can A/B easily. So, the jury's out, for my tastes. About to also mix it up even more with a Herron VTPH-2, just to see what a phono pre upgrade might offer....

Your vinyl set up is only as good as the weakest link. Instead of focusing on a $3k+ cartridge, work on isolation-cables and synergy between the cartridge and phono preamp.

You need a good tonearm. I had 2 10x5's that sounded good but are junk as far as construction goes. A highend cart won't do as well as it should without a good arm.