Network Card

I have a Sangoma FreePBX Appliance 500 and have a need to add an additional network card. I know that there are two PCI Express slots open on the system, but couldnt find a list of recommended Network Cards (found a list of expansion cards that were all telephony related T1 cards, etc…). In hoping to stick to something that is well supported I was thinking about this card (Intel EXPI9402PT) which utilizes the Intel 82571GB chipset. I am hopeful that the chipset itself is supported in the kernel, but apart from that I am not sure what the specs are for the pci express slots in the appliance. I cant find any documentation on the sangoma site as they seem to have removed any existence of it ever being sold. The best I could find was a youtube video from Chris at Crosstalk solutions doing an unboxing of the 500 appliance. The video shows that they exist but he doesnt talk about what speed they both support. Anyone know for sure? The NIC I picked out above is a x4.