The challenge is to make the fastest polygon island selection compound possible. Your compound has to work out of the box, as we don't want to install plugins, addons, workgroups or anything else (so I think you will need to rely on factory nodes).
I have attached my own polygon island compound along with a test object for you to compare performance. Please make something much faster, or pimp my existing compound
Depending on the island, my compound outputs the same polygon indices multiple times. I don't mind because it's not typically a problem for ICE Topo. If you prefer to output only unique indices, feel free to go for it. But it'll likely slow down your compound.
P.S.: Just in case you were wondering, the idea for this was proposed to me by someone on Vimeo after I asked for a fast polygon island compound in my latest video.