Software and performance
The Ultra runs Android 4.2.2 Jelly Bean, which is a couple of versions old now that Android 4.4 KitKat has made its public debut. It's disappointing not to see at least version 4.3 on board, given the high price you're paying for the phone and the fact that Sony isn't very quick with updates. In reality, however, you probably won't notice much difference due to the visual tweaks Sony has made.
It keeps the standard Android architecture -- multiple homescreens, apps in a grid of icons and six app icons along the bottom for quick access -- so existing droiders will feel at home. I wasn't particularly keen on the aesthetic tweaks though, or Sony's own photo and video galleries.
It's also allowed the homescreens and app tray to be displayed in landscape orientation, making the Ultra act much more like a tablet than a phone.
It's powered by a Qualcomm Snapdragon 800 quad-core processor, clocked at a mighty 2.2GHz. It achieved an impressive 3,550 on the Geekbench 2 benchmark test, putting it on a similar level to the Samsung Galaxy Note 3. Navigating around the Android interface is swift and responsive, while demanding games like Dead Trigger 2 and Asphalt 8 played with very high frame rates, even when the graphics quality was ramped to the max.
Sony reckons you can squeeze 16 hours of talktime out of the battery, but I think that's a little ambitious. In my own test, I found the battery to quickly drain away when gaming and didn't seem to hold it well when on standby either. If you keep the screen brightness turned down and turn off GPS you'll get a better time, but you should expect to charge it before you leave work if you want much power remaining for your night on the town.
The back of the Ultra is home to an 8-megapixel camera, which is a pretty big step down from the 20.7-megapixel snapper on the Z1. An 8-megapixel camera can still deliver brilliant results however -- the iPhone 5S's camera is superb -- but the Z Ultra didn't particularly impress.
On my first shot of St Paul's Cathedral, the photo is a little on the dark side (although the sky is well exposed), colours are rather cold and there's a definite lack of clarity on the brickwork on the buildings and on the water ripples on the river.
Moving inside, the camera achieved a decent exposure and colours were more pleasing, but it suffered from image noise in the shadowy areas. For quick snaps, the phone will do fine, but if photography is important I recommend considering the Z1.
It comes with the usual panorama and HDR shooting modes, as well as a burst mode and various scene modes. There's a front-facing camera too for video calling over Google Hangouts or Skype.
The Sony Xperia Z Ultra packs a good screen and an intensely powerful processor into a waterproof, slim body. That body is absolutely enormous though, which, while good for sitting on the sofa watching movies, really won't appeal to everyone as an everyday phone.
If you're after the largest screen you can find that will still just about fit into your pocket, the Xperia Z is worth checking out, but you might find its smaller siblings more usable.