Dunno how well it works for 100 megabit, but we've been using it successfully for 10 megabit for years now.

This should work for 100 as well. Gigabit is where it needs all 8 wires, and all my drops in the house are ready for gigabit, minus one. I found a bad run of cable, and ended up using it anyhow since the repair people left it in the wall. It had 2 pairs not functioning, so I used the other two, and did use it at 100 for a time. It is now marked for my empeg at my desk though, so it is only running at 10.