If you want to fan the flames of a pending console war where fans and developers alike malign each other in the name of brand loyalty, then this Edge article on which console has more power will do the trick.
In it developers who are supposedly developing games for both systems say that the PlayStation 4 is technically faster than the Xbox One. Several anonymous "high-level game development sources" tell Edge Magazine that the PlayStation 4 is currently around 50 percent faster than the Xbox One. Several describe the difference in performance between the consoles as "significant" and "obvious."
For starters they say that memory reads on PS4 are 40-50 percent faster than Xbox One, and its ALU (Arithmetic Logic Unit) is about 50 percent faster too. Developers said that unoptimized platform-agnostics builds of their games can run at around 30FPS in 1920x1080 on PS4, and "20-something" FPS in 1600x900 on Xbox One.
"Xbox One is weaker and it’s a pain to use its ESRAM," said one developer.
Another anonymous developer said that "the hardware isn't locked," and that both companies are still working on graphics drivers for each console. They note that "the Xbox One is lagging behind in this regard."
Microsoft "has been late on their drivers and that has been hurting them," said one source. Another sources described Xbox One’s graphics drivers as "horrible." Developers who spoke to Edge expect that these drivers will continue to be improved before and after the systems launch.
One developer told Edge that Microsoft has one advantage over Sony's system: "Let’s say you are using procedural generation or raytracing via parametric surfaces – that is, using a lot of memory writes and not much texturing or ALU - Xbox One will be likely be faster."
Interestingly enough, the developers Edge spoke to said that they would not go out of their way to support console specific features of each console such as the DualShock 4’s touch pad or Kinect.
"They really want us to make use of platform specific stuff to give their version a leg up over the other," said one source. "But unless there's a good design reason or incentive we rarely do."
Ultimately the takeaway from this Edge article is that - even if there is a vast difference in power - it's likely that consumers won't notice the difference between different versions of a particular title because most games will use platform-agnostic codebase.
You can read the entire Edge article here - be sure to read the comments as well, for some additional arguments on which system is more powerful.