They link to some benchmarks in the article: https://github.com/aspnet/benchmarks (they're a little hard to read on mobile, but I think the tl;dr is "plenty fast" (or to quote the article: "Our lab runs show that ASP.NET Core is faster than some of our industry peers. We see throughput that is 8x better than Node.js and almost 3x better than Go, on the same hardware. We’re also not done! These improvements are from the changes that we were able to get into the 1.0 product.")