There isn't a top xx down devices. There is "Devices with down Monitors" web resource that works exactly to what you're looking for, minus a limit you can specify.
You can also try a "Device tree, by properties" web resource and have the first property set to status. This will give you a space saving view at device status.
We use a smartgroup to display all the critical devices onto a dashboard view onto a screen on our wall, so we don't really have access to it. The dashboard works great for us and we use the following monitors CPU, Memory,Disk, Bandwidth, Battery and Temp.
Unfortunatly because we only view this screen "Device tree, by properties" does not work as its not expanded, and "Devices with down Monitors" displays nothing when using a smart group.
I've got around it by showing the smartgroups contents, I was just hoping to be able to show a percentage of down time next to the monitor