Rescan memory and CPU usage

> In the top snapshot I took above - cpu wait was only 3.3% but I'll try
> again to see if it varies much
>
> my cache/db is on the SD card (class 10) in the Pi
>
> my library is on a samba share on a NAS server (NTFS) on the same subnet

Most likely this is the bottleneck. You could try to attach a USB disk
directly to the Pi to see whether it makes a difference.

--

Michael