The XPS 13 was recently upgraded to Kaby Lake, so if you're fine with the smaller display, I'd say go for it, I've heard great things. Also, do realize that th

The XPS 13 was recently upgraded to Kaby Lake, so if you're fine with the smaller display, I'd say go for it, I've heard great things. Also, do realize that the UltraSharp model will have a significant impact on battery life. The comments I've looked at for the XPS 15 9550 (4K display) say that the battery life is basically halved, but it's supposedly still around 4.5 hours of battery life. If you prefer the 15-inch, you might want to wait for a while - they still only feature Skylake CPUs and I think an upgrade is imminent (given the recent XPS 13 upgrade and all.) I don't have any personal experience with the machines, but I'm planning to buy the XPS 15 once it gets an upgrade.