Ironically I've started a very very small Reformed fight with my anti-Calvin Lutheran arguments about the Eucharist.
To be honest, I don't think the Real Presence or Absence of Christ in the Eucharist is really an issue (as we Catholics don't even believe they have a valid Eucharist, so really it IS just bread and wine). The real arguments are:
1. How dare you say we don't have a valid eucharist! / Does confecting the Eucharist require Holy Orders?
2. Is the Eucharist a Sacrifice (the biggest question)?
3. Is grace bestowed (and venial sin forgiven) through the Eucharist