If you need another reminder that Sony is hurting in mobile, just take a look at the Xperia X Performance. It's the most powerful version of the electronics giant's new phone lineup, but rather than a full-fledged successor to the Xperia Z5 (itself a mid-range entry), it's more of a half-hearted attempt at staying relevant. But if you want the fastest Sony phone around, it's also your only option.

The Xperia X Performance is the most intriguing of Sony's new X lineup with its Snapdragon 820 processor, waterproof case, and 3GB of RAM. The base Xperia X only has a Snapdragon 650 processor, and the Xperia XA is even worse off with a MediaTekHelio P10 chip (along with lower specs all around). But, unfortunately, it's only rocking a 5-inch, 1080p screen, which is 0.2-inches smaller than the Z5 (as well as the same resolution). And while its 23 megapixel rear camera and 13 megapixel front-facing camera sound impressive, they're also the same sensors we got last year. Of course, we also loved the Z5's screen and camera, so perhaps Sony didn't need to change much after all.

Specs aside, the X5 Premium feels pretty great. At 8.7 millimeters thick, it's noticeably chunkier than the 7.1 millimeter thick iPhone 6S, but that also gives it a solid feel that I've grown to miss as flagship phones got thinner and thinner. And as always with Sony phones, its metal case gives it a decidedly premium feel. It's a phone that feels like it can withstand a few drops without falling apart, but at the same time it feels luxurious in your hand.

While it seems like the Xperia Z line is pretty much dead, Sony tells us it'll stick around at least until the summer. It's unclear if we'll actually see a new Z model this year, which means the Xperia X Performance is your best choice if you want the fastest Sony phone around. If you're looking for an even bigger and better screen though, along with improved battery life, the Z5 Premium is still worth considering.

Chris Velazco contributed to this report.