I have a Sumiko Oyster cartridge. MM with a 4 mV output.

Yea, I've checked around on Needle Doctor. Just wasn't sure if an upgraded phono preamp would provide significant volume. It sounds great as is so I don't want to shell out $500-1000 on a preamp just to get a small increase in volume.

Maybe a different cartridge with a higher output would be a cheaper option....