Suggestions about upgrading



I currently have a NetGear RN316 with 5x3TB hard drives with X-Raid giving me 10TB of Storage and drive redundancy incase on drive fails. But I am thinking time for an upgrade I take out one drive now and put in a larger drive say 6TB and slowly replace the 3TB with 6TB or should I look at going for one of the newer RN426 and stack that with 6TB or 10GB drives and then sell my RN316 (or keep to store snapshots of the RN426?)

I purely only use this NAS as a plex server, nothing else