Cartridge recommendation for classical listening

Low output model (0.7 mV) will need more gain than your MM input can provide. Also for LOMC you may need optional loading, 47k Ohm could work too, but any lower value from 100 Ohm to 47k Ohm is nice to have too. 

The output of your Sumiko HOMC cartridge is just like MM cartridges, this is why your MM input is fine with your 2.7mV High Output MC

But MM cartridge definitely can work better with your MM phono stage, it can be better in terms of sound with more advanced (user replaceable)
stylus profile than your Elliptical, but the output of MM cartridges also higher up to 5mV depends on the model. 

Anyway, step by step upgrade is a long process, enjoy your HOMC, you can always find something better in the future. 

I wouldn't mount a $1K cartridge on a P3. It's a nice turntable but I doubt you can wring enough performance out of that deck and tonearm to justify the spend. Others will surely disagree. If it were me I would mount a Nagaoka MP-500 and be done with it.

IMO, the London Decca cartridges and Ortofon SPUs are especially good for classical music. Both cartridge brands have models in their respective families for well under $1,000. But these cartridges will require tonearms that are compatible with their size, weight and resonance limitations.

The P3 has been extensively upgraded with nearly a thousand dollars in modifications.

In fact, I was amazed at what the turntable was capable of with this new cartridge.

I wouldn’t mount a $1K cartridge on a P3. It’s a nice turntable but I doubt you can wring enough performance out of that deck and tonearm to justify the spend. Others will surely disagree. If it were me I would mount a Nagaoka MP-500 and be done with it.

I think an investment in a good cartridge is worth it for any turntable, because that cartridge does not have to stay on one turntable, it’s a separate device. $500 or $1000 - doesn’t matter at all, the price does not indicate the quality directly. Cartridge can cost more than a turntable and it’s fine if the quality of the cartridge is nice.

What must be avoided is an inferior cartridges for more money if the lower price cartridge can beat it easily (only owner can decide for himself).