Well if you want to have a fast RAID 5 you will want a RAID card with a BBU to enable Write Back.
I am a LSI based fan (Doesn't have to be LSI would be like 3ware etc as long as it is a LSI Chipset). Their RAID cards are pretty superior to others and I know them well. You will end up spending a lot of money for a good RAID card. otherwise you can also find a used card that is SATA II still and you will be fine. SATA III only benifits on SSD's since HDD's still don't max out SATA II. I just got a LSI MegaRAID 8888elp with 512 MB Cashe and you can buy a battery for it. I have it running 3 RAID 0's and i get 250+ Read and writes on all the RAIDs.