Imec/Nokia had a technical paper last month, "Proposal for a 500GHz Silicon Photonic Modulator" that uses EO polymer.
Concluding sentence - "We found that achieving modulator bandwidths of hundreds of GHz doesn't require plasmonic waveguide design or CMOS-incompatible Pockels materials (TFLN and BTO)."
Edit - my summary will also have a part that mentions 400G per lane with and without plasmonics.