With a 0.4 mV output cartridge, you'd need about three times the value you suggested. I have owned several cartridges with this gain value, and I've always found 60 dB a good match.
There is no simple rule-of-thumb. It really depends on your listening habits, but even more it depends on the gain structure of the linestage preamplifier into which you feed your phono preamplifier output.
There is no simple rule-of-thumb. It really depends on your listening habits, but even more it depends on the gain structure of the linestage preamplifier into which you feed your phono preamplifier output.