So, if you're asking yourself, "why pay the extra dinero for a private tour"?, here's a short list:
1) Silvia (w/easitaly) is awesome! She's friendly, and personable.
2) You can put a bullet in my head before I take another one of those group tours with the headsets. If you find yourself standing in line without a "skip the line" tour, sure - go ahead and sign up with any of them. The price is worth skipping the line (often 3 hours). But once you get inside, ditch the group, hand back your headset, and open up the Rick Steve's app. It's pretty good on most tours. BUT DONT DO THAT HERE. Use Silvia.
Silvia talks to you one-on-one. You can hear her, and interact with her. You'll get much more info with her than with any other method.
3). If you have a question, you can ask. Can't do that on a group tour.
4). She moves at your pace. Not the group's. If you need to hit the restroom, no problem. Can't do that on a group tour.
5). This is a true wonder if the world. When will you be here again? You paid mucho dinero to be here - spend a little more to actually understand what you're seeing! I'm not saying you have to get private tours for everything. But this is not the place to skimp on the knowledge download. She's like a Vatican supercomputer. We peppered her with questions, and there wasn't a single "I don't know".
6). She explains not just the religious aspects of what you're seeing, but the historic, and political aspects too. You walk away with a really good history of Rome, as well as the Vatican, and why it's important to Catholics and non-Catholics alike. (As a non-Catholic, I've never understood the power of the Pope in history).
7). She comes with visual aids! She carries an iPad with drawings and diagrams to illustrate what she's talking about (like when she explains what things used to look like). It really helps to see a picture when someone talks. You can't get that on a large group tour.
8). We saw stuff no one else sees. In the Vatican Museum, we were often escorted beyond the ropes to see sections not on the other tours. We were able to see entire wings all by ourselves.
9) She picks you up at your hotel. Yeah, you can get a cab or bus over there, but why fight that? This gives her time to explain what you're gonna see, and prepare you a bit.
10). Did I mention Silvia is just plain awesome?