I switched backends a bunch of times because everything I tried (Go stdlib HTTP, Tornado, etc.) kept getting taken out whenever I would hit the front page, either due to CPU overload or some sort of resource leak. I ended up using Warp+Wai+Servant (https://github.com/yesodweb/wai) and it has been smooth sailing since then off my $3/mo VPS. It can take thousands of req/sec without flinching (which is higher than what you see from top of HN - that maxes out at a few hundred req/s).
Yes, I first tested locally with httperf and some other tools. I took it as a good sign when the load testing tools crashed before my server did. Then, I found a few services by searching for something like "website load test" and using their free tier (which would typically generate something like a few hundred req/sec - sufficient to simulate HN).
