Cartridge recommendation for classical listening

What’s surprising about my preamp is that at a ten o’clock setting the volume is quite loud. I’m wondering if the low output model might work better.
However, at this point I’m really enjoying the sound of this model.

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.