Rumor: There are 2 PS4 Neo SKU's, only one will make it.

[ChristianTheAtheist]

So, according to NeoGAF insider OsirisBlack, Sony is testing and internally debating 2 PS4 Neo SKU's from the beginning, one of them would use the Jaguar PS4 CPU with a higher clock speed and other tweaks at $399, this model would offer 4.2 TF performance, the other would use a new and better CPU at $499, reaching 5.5 teraflops of performance.

Also, the Neo form factor would require the use of an external power supply to prevent overheating.

http://www.gamepur.com/news/23460-massive-ps4-neo-leak-gpu-2x-more-powerful-high-clock-speed-55tf-price-499.html