I know own the XPS13 AND Surface Pro 4
The Surface Pro 4 is going back.
One thing to confirm from this review, is the "quiet" operation, even under load. I can report happily that, even within a game, the Dell XPS13 stays very quiet. You can't game with it on your lap without feeling that heat, but on a desktop, it is very quiet. This fan/noise tuning is pretty awesome, and I'd be curious to see a teardown that compares the thermal system to last year's model (9343). Perhaps it's just the old system, but with the Skylake CPU it can run at much lower speeds?
I think it's essential for an ultrabook to give off the impression it can handle maximum load without "sweating it". The Surface Pro 4 has a neat hybrid system, and stays dead quiet for most light tasks, but once you need to stress the internals to do normal computer things, it sounds like a miniature vacuum cleaner. The Dell XPS acts calm and cool under pressure. That's a must have and the main reason I'll be sending the SP4 back.
I will miss Windows Hello dreadfully though!
To those wondering - you CAN charge the Dell XPS 13 through it's USB-C port. To meet the standard for USB-C/Thunderbolt, you HAVE to support all parts of the standard, not just pick and choose. The only chargers available on the market are the one for the Macbook and the Google Pixel 2's charger. I currently have the Pixel 2 charger on order, but I've read user reports from trustworthy sources that it works just fine to charge the Dell.