Cartridge-- M/M or M/C

Scottht,
With your current setup I'd recommend to "chill out" about looking for another cartridge since Eroica is one of the best ones in $500 range(especially if you have a possibilitity to change the load of your phonostage). It's very hard to beat with any MM cartridge unless priced very high. There are two types of Eroica one is with .5mV(L) and another is with 2.5mV(H). For L you should have an expencive high-gain phonostage with at least 60dB of gain. For H 50...54dB is enough.
I set up an analogue rig to my friend from Oracle Alexandria, stock RB250, Goldring Eroica(new $220) and Michell ISO phonostage used designed by Tom Evans. This setup gives a perfect accuracy, presence and descent bass.
The other great thing about probably all of goldrings is they track so damn good no-matter what.
Think of probably upgrading phonostage or any other of your components instead.
Happy tunes!

Since the conversation had went towards decks,
I'd say my understanding on that issue:

Collector DC motors have the largest chaotic electro-magnetic noise. Under chaotic I assume freequencies of a different spectrum with no exempt to transients. Please note, MC cartridges are less affected by such noise thus perform more quiet and more accurate.

AC motors have significantly smaller noise but fully or mostly depend on power-line freequency stability.

Quartz digital motors have even less noise than AC motors thus the most suitable IMO in analogue turntable applications. Yes, DD tables could sound better depending on its construction since the quartz motor influence factors out compared to DC collector motors.

What about belt-driven tables with quartz-digital motors? Probably VPI does that so-far...?

The brushes of DC motors are the main culprit of EM noise. The motor rotates from the physical contact from the brushes-collectors and due to physically unstable contact the transient EM noise occurs while the motor is working.
To visualize or audiolize that effect larger you can bring a drill(corded or cordless) closer to the cartridge and turn it on. You may even see your speaker drivers moove picking up transient pulses. Certainly such are much smaller from the supplied motor but they're present and definitely affect the performance of the system.
Cartridge pickups, microphones and speakers are working on the same effect of electromagnetics. when the current flows through the conductor it induces a magnetic field and bacwads: the moving magnet inside the electric field creates emf i.e. electro-motive force. One way or the other all magnetic systems are vulnerable to EM interfearance.

In AC motors there are no collector brushes and so is EM noise is minimized. The quartz-digital motors we can consider as a special case of AC motor where the freequency of pulse is dictated by quartz.

I never compared or analyzed issues of stability of EM interfearance, but more often myself had issues especially in cheap analogue systems where the system picked up too much of the motor noise that had been a primary reason of poor cartridge performance.

Without looking inside of your Lenco motor which is I guess an advanced tech stuff, I can't say wether it's idler-wheel, AC or digital one.
If you're saying that the motor doesn't physically contact the brushes, than I assume the motor is driven by magnetic field that could either be due to the AC or quartz clocking pulse.
I can also assume that there are no brushes and ball bearings instead. In this case the noise will be much smaller but the fact of surfed contact is present still...

The drill example is only an example of an open problem arround all DC motors. Certainly there are ways to tame such noise and make it's influence area much smaller.

AC motors while do have vibrations have much less EM noise than DC ones. Kill one bitch and another will rise.

EM noise can interact with cartridge's magnet and change it's specified properties almost as well as Vibrations and speed instability.