My guess is that the term silicon refers to the insulative coating around the actual wire not the wire itself. I am of the opinion that all Bosch wires are copper with resistors on the ends as MB did it in the first place.
They ought to be fine, but so were the originals. The wires themselves very seldom fail. The resistors are another story and could be bad out of the box. The only way to tell is to watch the firing voltages on an ignition scope. Oh.... the other way is to replace them and if there are no bad ones in the box; substitution is a diagnostic process. (the most expensive of course).
I haven't measured the resistance of a plug wire in at least 20 years. It may be good for writing a thesis but plays now use in modern diagnostics. Too many ways for the results to infer the wrong thing! Both good and bad.
Bosch Master, ASE Master, L1
33 years MB technician