RAM is cheap...stick with 8GB, just because you can. 
However, I agree that the CPU could be dropped down to an i3/E3 and still have great performance, if this box is purely for file storage. I run my 9261-8i and HP SAS Expander in a box with 8GB of RAM (going to upgrade to 16GB for the hell of it) and an E3-1220v2, and it does great. It's a quad core with no HT (the E3-1230v2 has HT). If it's purely for file storage, venture down FreeNAS...or some NAS specific OS. If you plan to do anything else, go with WHS (local PC backups being the big one, IIRC...WHS can do this great, and I don't think FreeNAS can).

However, I agree that the CPU could be dropped down to an i3/E3 and still have great performance, if this box is purely for file storage. I run my 9261-8i and HP SAS Expander in a box with 8GB of RAM (going to upgrade to 16GB for the hell of it) and an E3-1220v2, and it does great. It's a quad core with no HT (the E3-1230v2 has HT). If it's purely for file storage, venture down FreeNAS...or some NAS specific OS. If you plan to do anything else, go with WHS (local PC backups being the big one, IIRC...WHS can do this great, and I don't think FreeNAS can).







