Since you asked, I will give you my opinions.
(Remember, these are my opinions, based on my sonic tastes.)
One, I would consider getting a decent tube preamp. Look for one that will accomodate both a MM or a medium output MC. (i.e. it has around 50-55 db of gain.)
I recommend a used ARC PH-3. They are a little bit noisy, being a tubed preamp, but since you already use a tube preamp, this will probably not be a problem for you. (On the other hand, it was a problem for me. I am particularly sensitive (overly sensitive perhaps?) to tube rushing for some reason, so I have gone the solid state route myself. The sound of the ARC PH-3 is very good, and used you can usually pick these up for around $700-800, and they have 54db of gain, if memory serves, which means it will work fine for MC cartridges with outputs of 0.4-0.8 MV or more.
Two, As far as the cartidge is concerned, I recommend that you contact Briankutch about his Koetsu Black that he will be selling for $500. (It would mate nicely with the ARC PH-3 by the way. I know this, because I had exactly that setup!) FYI, the Black is not without its limitations. It has a slightly rolled off treble (not bad mind you, just very slightly rolled off, and if you had nothing to compare it too, you might never really notice), and the bass is a bit loose (this is more of the limitation, as it is not deep and tight, and if you listen to classical music or jazz, you might be concerned. It works fine with Rock 'n Roll, IMHO, as the bass is there, it is just not incredibly deep and tight. But for Rock, who really cares?! And I say that as someone who listens mostly to Rock.) On the other hand, the mid-range of the Black is classic Koetsu. It sounds incredibly lush, especially for vocals. (I will point out that I am a fan of Koetsu cartridges, so you can take my recommendations with however many grains of salt you like.
An alternative would be the Shelter 501. It has better frequency extension than the Black, but not as good a mid-range, IMHO. It has a very good mid-range though, one that is just a bit more neutral. Used, you can probably get the 501 for around $500. (It is a tossup as to which cartridge I would get for $500.) The one nice thing about the Koetsu line is that they have a lower noise floor, so the music has a blacker background. (The Shelter is good, just not Koetsu great in this regard.)
FYI, I currently use the Shelter 90X. A very good cartridge, as it has great frequency extension, espeically in the bass response, and very good, almost a great, mid-range. I prefer it slightly to the Koestu Rosewood Signature I used to use, because of its bass response. (Although, the Koetsu had a great mid-range, very good treble extension, and good bass response.) But the bass response on the Shelter 90X is tough to beat, IMHO. Someday, I will find a cartridge that combines the bass response of the Shelter, with the mid-range of the Koetsu line. (I have heard that the Koetsu Jade Platinum does, but that is WAY beyond my price range!)
Three, and this is the most important piece of advice! Get a RCM. Even a cheap Record Doctor or a Nitty Gritty (which is what I use), will do a good job on cleaning the records. You'll also need a set of decent brushes (the disk doctor brushes are good), and some RCM cleaining fluid (I recommend the Record Research Lab (RRL) Super Vinyl Wash, and most of the people here use it.) Having clean records is very important, as it allows you to remove all the grundge in the grooves, which means a quieter, blacker background to the music.
Well, those are my thoughts.
Good Luck in your quest!
