I agree about the choice of NIC - always go for Intel. The onboard Realtek connections are not up to the job for heavy work.
Not true. Realteks are fine for NAS work if they are PCIe
. While far from high end, the current crop of 81XX realteks are lightyears better than the old 80XX ones. My server can easily max out gigabit with it's onboard Realtek (980-990 mbit/sec in iperf). Even my Atom board can push more out of it's onboard Realtek PCIe then a server class Intel in the PCI slot. The bus used is far more important than the chip. Problem is that not every onboard NIC is actually PCIe, but that is not a problem specific to Realteks.
Now, a PCIe
Intel is of course better in that you will get lower CPU use without sacrificing throuput. If CPU time is really critical to you then get one. But getting a PCI (no "e") Intel is going to hurt raw throughput compared to a PCIe Realtek and throughput is usually what one wants in a NAS.