I didn't explain why clustering helps?

Again, it makes such a network scale about 5 to 20 times more because you're hitting all UltraPeers at every hop along a search path. That's 5 to 20 times more files you can find. That's a huge difference. Clustering makes a better network, which is what we're all trying to do. Maybe you should implement the open UltraPeer protocol in your own client?