In general I wouldn't expect the difference to be significant. The VerilogA code is compiled to C (at least parts of it) and that may give some small speed benefits for the spectre engine - however, the analog parts of VerilogAMS are also simulated in the spectre engine. So there are differences, but it should not be massive - and in most reasonable circuits I wouldn't expect there to be a difference. In essence, the AMS simulator is a single simulator which uses both a digital "solver" (the event-driven Incisive engine) and an analog solver (spectre, APS, XPS-MS, or UltraSim).

It may make sense to contact Cadence to take a look at your specific examples to help understand what the difference is - or if it's small enough (and you can share it in public), share the example here?

Regards,

Andrew.