Best wishes on liking the 600 as is! I've enjoyed a lot of Stanton/Pickering cartridges over the years when they were still being produced, but I don't have any experience with after-market styli for them.
As to cartridge upgrades, I'm not too sure that higher-cost cartridges make me any happier with my records. My first experience with a Stanton 500E was about 35 years ago, mounting that up as a stand-in while my 981LZS was shipped back to Stanton for repair, and the much cheaper cartridge still made me want to keep playing one record after another. Twenty-one years ago, I had four Stanton 500 bodies serving all my needs: a 500E MK II on an LP12/Ittok rig and three more 500 bodies for a Stanton STR8-80 turntable, each on its own headshell and with different .7 mil, 1 mil, and 2.7 mil Stanton styli for various purposes. I never thought that my musical satisfaction was at all impaired just because I was using Stanton's cheapest cartridge line. Currently, and for most of the last 4 1/2 years, an AT3600L has kept me happily spinning records on a daily basis.