Regarding SATA3 support, the only instance that you are going to feel a difference vs SATA2 is when using an SSD.
WIth that in mind, I would consider getting something like the ApricornVelocity Solo X2. Basically the card uses a PCIe 2.0 2x slot and you mount the 850 EVO SSD on the card for full SATA3 bandwidth. Its tried and tested and also a clean way to install your SSD. It also gives you an additional SATA3 port should you wish to connect another SSD or HDD.
There is also a Duo version ofthe card - with that you forgo the additional SATA3 port but instead can mount 2 SSD's on the card, configure them in RAID 0 and get speeds of up to 800MB/s.
In general, if I had a Z600 which I felt like upgrading I would probably get one of the above two cards, also a USB3 controller card if you do not have this already, something like the HighPoint RocketU 1144C, for full bandwidth on all USB 3 ports.