Agree with the recommendation for Synology; they're hard to beat on value although you can find cheaper NAS boxes. I presently have both a DS207 (1TB) and a DS211 (6TB), and they work like a charm. Both are configured with a pair of disks in RAID0 so they're fairly quick...
I also definitely recommend Synology NAS solutions - very capable machines and the company is committed to follow-up with their software updates. You buy the NAS now, and as they release continual updates to their firmware, it just gets better and better "for free".
On the other hand, I would never recommend running a NAS with disks in RAID0 - you run a NAS to store your data and to be completely reliable, I configure my DS508 in RAID5, and if I was running in an enterprise with a DS1512+ then I would certainly consider running in RAID6. I have "lost" a disk in my RAID5, and the NAS rebuilt easily once I replaced it - but if you lose a disk in RAID0, then wave goodbye to your data. Unfortunately disks are not 100% reliable, and the speed increase means nothing as soon as you start accessing the NAS over a network.
-- Pete.