Thank you! Like you, after the update, I only had 6GB of 128GB available after the iOS 11 update. I independently let Apple reduce the size of the photos stored on the device to free up room for new screen recordings, which left 81GB free. Now, it is
much better! Lag of a second or two, which is acceptable, instead of 15 seconds or more!

I'm feeling better about the update. Maybe the Apple Watch will become more responsive as well, with more room on the iPhone! The Siri issues may have been due to server overloads. We shall see. However, 90% of the time, Siri on the cellular Watch still wants me to use my iPhone to get the answer!