Does your motherboard have open-ended PCIe slots? You can technically plug any PCIe card in an x1 slot, but on a lot of motherboards that involves cutting out the plastic that closes the "end" of the x1 slots. Personally I use a couple of these JMB585 cards in x1 slots to get PCIe3 speeds which helps with bandwidth during parity checks.

ETA: You can also look into JMB582 or ASM1064 cards if you don't have open-ended slots. Both run at PCIe3 speeds so they're double the bandwidth you'll get out of a Marvell card.