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.