My answer was based on my interpretation that the builder had only run a single 16/4, so you would need to wire a pair of speakers together. Of course, it would give you more flexibility if he ran two sets of wire, so that you could reconfigure the speakers later. If so, and we again assumed 8 ohm speakers, then we're talking 9%, which is still above the recommended 5%.
Now, I don't know how important that 5% number is. We all understand that the added resistance from the cable will attenuate the signal some, but that in itself is not a problem. My understanding is that, as the percentage of cable resistance goes up, it will attenuate different frequencies more than others, based on the fact that a speaker's impedance varies with frequency. In other words, the increased cable resistance affects the speaker's frequency response. Of course, electronics that provide equalization can fix that, and depending on the speaker, it might not be an issue at all.
If it was my home, I would:
Do exactly as you are, with regards to a wiring closet.
Stick with the 16/4, but add another run so that each speaker has its own connections in your wiring closet. That will allow you to balance the volume later.
If I was really picky (which I am), I would have a system with EQ, and flatten the frequency-response and tune for the rooms.
As far as the Sonos is concerned, it is true that one of its strengths is wireless, and that they charge a premium for that. But their wireless controller might make it worth that premium, even if the rest of the system is hardwired. Personally, I hardwire whenever I can, but a wireless controller is a must. I'm currently setting-up my iPad as a controller for my myriad of Audiotrons
. Maybe I would go with Sonos if I could bring myself to pay that much. Being cheap, I live at the trailing edge of technology.