Depends on availability of PCI-E lanes and resources in PCI-E v. 3.0, I think. I don't even think there would be a limitation under PCI-E 2.0, or it would be marginal -- <= 100MB/s. PCi-E 1.0 will cut the bandwidth to just more than half of that, I think.
You're best to use an PCI-E SATA-III card in circumstances such as those asserted by REDZO. You're best to use the onboard controller, unless you need more SATA-III ports than provided on your motherboard, as with my Z68 systems. I think Z77 was similarly limited -- I just built one of those.
I think your 4-port SATA-III card would be either a PCI-E x2 or x4 card. So the slot where you put it should be fully capable for it. With my mobos, I'm fine with 2x SLI, but that leaves me a slot of x16 size which can only configure as x1, x4, or disabled, depending on what other features are consuming resources or enabled in BIOS. The x4 configuration would allow for a PCI-E x2 controller or device, as well as x4.
In order for me to add such a 3rd PCI_E card, I would need to turn off my Asmedia USB3 controller and my Marvell 2-port AHCI SATA controller. I don't need the latter, but I want the USB3. So my workstation "configuration" is deliberately limited to the onboard ports. If I want more, I could enable the Marvell controller -- which gives me two ports and only in AHCI mode for SATA-III.
Of course, some of us who've used the ONBOARD Marvell controller are less satisfied with the results. But figure my Intel ports include two cabled and available ports for hot-swap bay and front-panel eSATA ports. I have a port for my optical drive, so all six of my Intel ports are "taken," but two are available for mobile drives.