Direction on my next upgrade

Take any advice you like best from this smorgasbord, but don't spend money on Synergistic Research tweaks, as Millercarbon suggests you do.  Most of those tweaks are "controversial", at best, in terms of actual benefits.  I am not saying categorically that they are worthless (although that is my private opinion), I am saying that such items are best reserved for those in a more advanced stage of audiophilia and system development. First, learn what you like and what it takes to get your system to a point where you are generally satisfied. I wouldn't be so bold as to tell you how to do that, because I have no idea what you are seeking SQ-wise. After that, maybe think about PHTs and HFTs and the like, marketed by SR.  Their only saving grace is you can return them for full refund within an allotted time period.

@ millercarbon
Have you used this Raven amp that you always recommend? Why do you think it is so special over many other amps that are on the market?

Chakster, that article is from 1994. I think you need to catch your breath, relax, get stoned and listen to music for the sheer enjoyment of it.
Modern moving coil’s moving systems have much lower effective mass than back then. That old high end peak is long gone. Phono amps have also made great strides. The very best cartridges are MC.

@mijostyn
I have many LOMC cartridges and many different phono stages and SUTs and Headamps in my studio, so I am able to compare everything myself. The golden age of analog is NOT today, it was in the 80’s on its peak (for cartridges, turntables, reel to reel, speakers ). Actually for the speakers it happened earlier.

I owned two 681EEs and the Charisma run circles around them. It also tracks better by a wide margin. So Chakster, saying modern MM cartridges can not compete with old ones is patently wrong.

681EE is not even close to the best Stanton cartridges, because the stylus tip is Elliptical, the best Stanton/Pickering are all have Stereohedron and Stereohedron mkII diamonds (the greatest profiles in the history). Cartridge in the TAS article is 881s (Stereohedron) is not the top model, there are also Technics 100c mk4 and Audio-Technics AT-ML170 and those two might be better than Stanton 881s for someone (personal preferences).

I hope you can buy this new TOP WING to tell us how good it is, the price is just about $12500 for this MI, i’m sure you will like it. Especially when they will charge crazy amount for re-tip.

I would be willing to bet that there is no vintage MM cartridge that can compete with the Charisma never mind Grado and Soundsmith. They just did not have the materials science then that we do now.

You never tried the best vintage MM or MI, let’s face it first.
They had better materials not even available today for cartridge manufacturers like Beryllium for example, I just don’t want to repeat it all over again.

But having all those "ultra nano" materials today why only a few manufacturers can make a decent sounding tubes ? Tube are much simpler design than a phono cartridge, but many people prefer NOS from the 40's/50's than brand new tubes. 

Just compare the size of the Charisma’s diamond to that of the 681EE. It is easily 1/4 the size. The 681EE cantilever is a baseball bat in comparison.

Why are you refering to 681EE, compare your cartridge to 981 or SC-100 WOS and you will hear the most involving sound ever.

681EEE is entry level model, Stanton made so many models, some of them are cheap crap with conical styli.

Now maybe vintage cartridges are better than modern ones at the same price point, I can’t say.

Exactly
I want to remind you that OP asked for an "MM in the $500-$750 range " !
Not $2000

But, the Charisma runs in another universe. It also costs $2000.00 which brings another subject to mind. If you can make a cartridge with the same cantilever and diamond as a $16,000 cartridge for $2000.00 why does that cartridge cost so much??

I have no idea, got too many vintage MM cartridges with Boron Pipe cantilevers, Sapphire or Ruby, Titanium or Ceramic cantilevers. Some of them are $700, some of them are $3000 today.

IMHO the best MC cartridge you can buy is the Ortofon Windfeld Ti price considered. Add a Clearaudio Charisma and you have the best of both worlds.

I have an Ortofon MC 2000 new in the box, very special LOMC cartridge.
The Clear Audio is buying cartridge generators from Audio-Technica. I already have the best Audio-Technica MM ever made (the AT-ML180 PC-OCC with Gold-Plated Beryllium cantilever, later replaced with Gold-Plated Boron cantilever).

MM cartridges designed way back and the ClearAudio is nothing in this world of the best MM.

I gave you the link to $12500 Coreless-flux modern Ultra High-End MI cartridge from the Japanese brand Top Wing, do you know this brand? Recommended by Jonathan Carr a few years ago on audiogon. The engineer of the Top Wing used to work for the Grace back in the days. The Grace cartridges are amazing (F14 and LEVEL II series).

Have you used this Raven amp that you always recommend? Why do you think it is so special over many other amps that are on the market? 

I have a stellar record when it comes to figuring out what is good based on reviews and comments. Read willgolf, he had a Reflection MkII. Then watch this https://www.youtube.com/watch?v=Gcd76DZmbdY