A couple of opinions I would like to make.
One, you were the lucky guy who just snagged that off Audiogon, huh?! (Great price.)
Two, it appears to me, that you are running a very, very good turntable, with a very good tone arm, and yet you are using merely a good phono preamp and a pretty good cartridge. I think you need to upgrade both myself of those first. (The rest of your system is very impressive, btw!)
In fact, I think you should get the phono preamp first. I would recommend getting a used Aesthetix Rhea. These go for around $2,500 used. (My opinion is to not skimp on the amplification end of things, and judging by your choice of the Viva, I appears you agree that amplification is very important.) There are lots of other phono preamps that sound as good, or almost as good as the Rhea. However, very few are as flexible, and as easy to use as the Rhea. (You can adjust both the gain and the loading, from a remote control, so you can really dial in whatever cartridge you happen to be using. And since picking a cartridge is really a matter of taste, it might take you two or three or more to finally find your "perfect" cartridge. This will facilitate your search.)
In trying to keep with your budget though, (and to answer your original question), I would suggest a used Koetsu Rosewood (or better yet, a Rosewood Signature). These can be had for around $1,000-1,200. Or if you can stretch it a bit more, a used Shelter 90X can be found for around $1,500. Both of these cartridges are a bit on the warm side, especially the Koetsus. (The Shelter 90X will do justice to this system, as it has really good frequency extension, and it has really good mid-range. The Koetsus on the other hand, not great frequency extension, especially in the bass, but they have that mid-range magic that will charm you.)
Anyway, my opinions on the matter.
Good Luck in your search!
One, you were the lucky guy who just snagged that off Audiogon, huh?! (Great price.)
Two, it appears to me, that you are running a very, very good turntable, with a very good tone arm, and yet you are using merely a good phono preamp and a pretty good cartridge. I think you need to upgrade both myself of those first. (The rest of your system is very impressive, btw!)
In fact, I think you should get the phono preamp first. I would recommend getting a used Aesthetix Rhea. These go for around $2,500 used. (My opinion is to not skimp on the amplification end of things, and judging by your choice of the Viva, I appears you agree that amplification is very important.) There are lots of other phono preamps that sound as good, or almost as good as the Rhea. However, very few are as flexible, and as easy to use as the Rhea. (You can adjust both the gain and the loading, from a remote control, so you can really dial in whatever cartridge you happen to be using. And since picking a cartridge is really a matter of taste, it might take you two or three or more to finally find your "perfect" cartridge. This will facilitate your search.)
In trying to keep with your budget though, (and to answer your original question), I would suggest a used Koetsu Rosewood (or better yet, a Rosewood Signature). These can be had for around $1,000-1,200. Or if you can stretch it a bit more, a used Shelter 90X can be found for around $1,500. Both of these cartridges are a bit on the warm side, especially the Koetsus. (The Shelter 90X will do justice to this system, as it has really good frequency extension, and it has really good mid-range. The Koetsus on the other hand, not great frequency extension, especially in the bass, but they have that mid-range magic that will charm you.)
Anyway, my opinions on the matter.
Good Luck in your search!