I also have the Xperia Z1s and the Xperia Tablet Z2.
A 5" phone with 1080p display is a lot more useful than even the Nexus 4 720p display. You can check maps, do light Web browsing and check email. But you do not want to answer email on a 5" phone, even with a Bluetooth keyboard. You want at least 7" 1080p to watch movies or do serious Web browsing, or to read ebooks.
The XPerias both can be charged with a magnetic dock. This is the only substitute for Qi that I find acceptable -but Qi is definitely better.
When you also have a 1080p phone the value of fitting the N7 in your pocket is reduced. But you really want to minimize the extra weight. The Xperia tablet Z2 is great at that, the Samsung Tab S is just as light, has an even better screen but lacks any form of a charging dock.
The tablet Z2 is certainly faster than the N7, but it is extra speed that you mostly use when running benchmarks. The brighter/crisper/larger screen is the main benefit. (that and the 128 Gb SD card).
If I hadn't upgraded already I think I'd wait to see what the 8.9" Nexus ends up looking like.