If you go to newegg.com /every/ desktop and mobile CPU they sell is sufficiently powerful to handle NAS duties. Usually in this situation the concern is not brute strength, but efficient power and heat compensation strategies because the NAS is going to stay on for long periods of time and may be locked in a closet where heat could become an issue. Purchasing an i5 or i7 for a NAS would be shooting gnats with shotguns. I would suggest looking for a cool, inexpensive chip that can run for months without costing a lot on your electric bill. Read the CPU reviews at newegg and they will tell you whether the chip runs cool. I suggest you pick a chip that has at least 20 reviews to get a fair assessment of the cpu. There is no reason why you need to spend a lot of money on this type of build.