How accurate is the s-parameter measurement for extraction

That's a bit of a strange question, since they are doing totally different things (well, assuming I've understood what you mean by s-parameter measurement). If you're asking about s-parameter simulation in a circuit simulator, then that is just running a simulation based on extracted models (or fitted models). An EM solver is doing an electromagnetic solve based on the field equations from the geometries and materials involved in the structure. If by "s-parameter measurement" you mean measured data in the lab, that rather depends on how accurately the measurement was done; similarly the accuracy of EM solver rather depends on how that was set up, which solver was used, and so on.

So I don't really understand  your question. I'm not sure you understand the question either, since it doesn't really make sense?

Regards,

Andrew.