PCIE 2.0 is double that so PCIE 2.0 x1 is 4Gb/s of Bandwidth available which is more then enough to run a RAID array of conventional hard drives. Yes adding more drives will theoretically make it slower , but as long as the controller has a good command queue and the drives are fast enough it will barely be noticeable performance loss.
OK thanks. I don't think the card I linked to was 2.0 though, I think it's just regular PCI-E x1.
So if you have say 6 slots on the mobo vs. 6 slots on the controller card, then an array with 6 drives would be faster if it was connected via the mobo instead of the controller card? But, the difference would probably not be big?
What about PCI (regular, not express) - what is the bandwidth of a regular PCI slot, and which controller card would be faster - a PCI one or a PCI-Express x1 one?
The difference would be very minimal for mechanical hard disks RAID since they can rarely saturate even a PCI-E x1 slot, since a PCI-E 2.0 x1 is about 5x more bandwidth than the fastest mechanical hard disks can use.
A single PCI slot provides 266MB/s which is also higher than what a mechanical hard disk needs, but if you intend to use more than 1 hard disk through the expansion slots a PCI-E slot would be recommended.