Cartridge upgrade for Goldring GR1.2 turntable

I have a friend who bought a Goldring GR1.2 turntable on closeout from Audio Advisor (about $216) on my recommendation six years ago. The GR1.2 is pretty much a Rega RB2 clone or copy, and from what I've been able to find out, came with a Rega RB250 tonearm and Goldring Elektra cartridge.

He recently got a Marantz PM8004 integrated amp, which, if you're not familiar with it, is pretty fabulous at its $999 asking price and includes a MM-only phono section of a bespoke design using discrete components. He's really enjoying the improvements, but it's kicking off an upgrade bug to bring the rest of his system up to the same level.

So he's looking to upgrade his speakers from Klipsch Heresys and wants to get a better cartridge as well.

I don't think he's going to consider carts above $500, nor LOMC carts because he'd need an outboard phono stage or stepup device. Based on the RB250's 12g effective mass and 4-11g range of cartridge weights, my short list of upgrades are the Audio Technica AT150MLX, Grado Reference Platinum, Grado Prestige Gold, Nagoaka MP-150 or MP-200, the Goldring G1012GX, or the Ortofon 2M Blue or Bronze.

Are there any good candidates I'm missing or is there a standout among the ones I've listed?

Thanks.