Given the quality of your amps/speakers and size of record collection, I personally think you would get more enjoyment from your records by upgrading the whole turntable.
There are some great deals out there at the moment - for example Music Direct are specialling out the Rega RP8 for $1995 ( outgoing model, $1000 discount ) - brand new and ready to go. You can get a better front end second hand but why not avoid the hassle. Buy a Rega Exact and it is plug and play.
If you decide to upgrade the cartridge for now I would stick to MM/MI because they are less demanding of the tonearm ( which on the AT is not a world beater ). My recommendations in your price range would be
Soundsmith ( these are excellent at all price levels - very smooth, detailed and musical ).
Nagaoka
I prefer these to both the Ortofon MM's and Sumiko's.
Whilst the AT MC's do perform well for the money, you wont get the best results with the AT arm.
There are some great deals out there at the moment - for example Music Direct are specialling out the Rega RP8 for $1995 ( outgoing model, $1000 discount ) - brand new and ready to go. You can get a better front end second hand but why not avoid the hassle. Buy a Rega Exact and it is plug and play.
If you decide to upgrade the cartridge for now I would stick to MM/MI because they are less demanding of the tonearm ( which on the AT is not a world beater ). My recommendations in your price range would be
Soundsmith ( these are excellent at all price levels - very smooth, detailed and musical ).
Nagaoka
I prefer these to both the Ortofon MM's and Sumiko's.
Whilst the AT MC's do perform well for the money, you wont get the best results with the AT arm.