Best Raid Controller Card for home media server?

I'm looking to get a Raid controller for my home media server. My current setup is as follows -

Motherboard - MSI GF615M-P33
CPU - AMD Athlon II X2 240 (AM3 socket)
RAM - 4GB
System Drive - Kingston 120GB SSD
Storage Array - Three 1TB WD Green drives in a Raid 5 array using the onboard Nvidia software raid controller

At this point my raid array is almost full, so I'm looking to upgrade the drives to three WD 4TB Red drives and connect them to a hardware raid controller card that is capable of RAID 5 or RAID 6 and can connect up to 8 SATA drives to it.

I'm not sure what Raid controller card to get. I was looking into the Adaptec 5805 controller card. It has most of what I'm looking for (4TB drives are compatible with firmware upgrade), but I've read it doesn't work with UEFI motherboards. My current motherboard is not UEFI, but I do plan to upgrade the MB in a couple of years time so this card would not work for me. I've also read about issues with the PCIe slots. Most Raid cards I've seen are 8X slot speed, but I'm not sure if it would work in a 16X slot. Also, most motherboards have 16X slots that are generally designed for graphics cards. Would an 8X Raid card work in a 16X slot that normally handles a graphics card?

I am planning on upgrading the motherboard, cpu and ram in a few years, but right now my storage capacity is so low and my funds even lower, I only want to upgrade the storage array at this time.

Any input, examples, or suggestions you may have would be greatly appreciated.

Thanks