Why do you need four SATA 3 ports? Are you aware that even the highest speed enterprise hard drives (HDDs) max out at ~200 MB/sec throughput, still way below the SATA 2 limit of 270 MB/sec?
The fact is you only need SATA 3 for an SSD, because a good SSD will be bottlenecked by an old SATA 2 port.
As you're proposing to run a NAS I'm assuming you're looking to run 4x HDDs, or perhaps 1x SSD (for the OS) plus 3x HDD. In that case I would recommend looking at the ASRock Q1900-ITX or ASRock Q1900DC-ITX (the difference is the "DC" has a built-in fanless PSU and runs off a laptop power brick) as they have 2x SATA2 and 2x SATA3. There are other options as well, but I hear bad things about the Gigabyte offering - they can only boot to Windows 8 until you update the BIOS, which requires installing Win8 in the first place... which is a pain. They also have some issues with Linux based NAS OS like FreeBSD I hear, something about kernel panic... I'm a Windows user so I'm just regurgitating what I've heard
Yes I am aware of the issue that mechanical HDDs are not fast enough to max out SATA2 ports. It was kind of OCD...I feel uncomfortable if I connect an SATA3 HDD to an SATA2 port. I guess I would have to get rid of this...
Maybe I will go for a J2900 mobo. I also have an eye on new AMD AM1 products, they are quite competitive, but TDP 25W...not so sure.
And this is quite important: if that mobo or CPU has poor support to linux system, that would be an automatic pass.