Akram El Assas has written up a performance comparison of dygraphs and a few other HTML5 charting libraries over at CodeProject.
dygraphs has always been written with large data sets in mind, and so it does quite well on these benchmarks. The one million point benchmark is particularly good:
dygraphs was the only library to complete the 1M point benchmark on 3/5 browsers, and was 6x faster than the competition on one of the others. There are a few tricks that we use to keep dygraphs running fast on large data sets. These are mostly under-the-hood, but they'll be great fodder for a future blog post.