Upgrading my home server, what CPU?

I have been running a little home server for a long time. It currently has an Intel celeron G1610, and a case that fits a Mini-ITX motherboard. It also has 3 big disks for data (NAS style), and one SATA SSD for the OS (Debian).

But lately I've been asking a lot from it and it's not really keeping up so I'm thinking to upgrade. A relatively low power consumption is important to me.

What CPU would you recommend?