Congrats on the charity ride!!

I"m quite happy with my WSD Madone. The most important thing is to find a bike that is the right size and geometry for you. For that, I think testing a base model would be sufficient. You just wouldn't know how the bike feels with higher level components, e.g., if shifting is smoother or different wheels help you ride faster.

I think the Silque is a updated version of the Domane, which is a different frame from the Madone, built with a bit more comfort in mind. A male friend has a Domane and he does find that it handles differently when cornering compared to a more race-oriented bike, though he seems to like and rides it often. You might want to try a Madone as well as the Silque to see if they feel different to you.