Here are the results:
|K-Meleon||Otter QtWebKit||Otter QtWebEngine||QupZilla||Midori|
|HTML5 Test||467 pts||399 pts||525 pts||400 pts||341 pts|
|Octane Benchmark||5915 pts||1222 pts||6653 pts||1285 pts||806 pts|
|BrowserMark||1590 pts||1165 pts||1926 pts||1052 pts||149 pts|
|RAM at startup||35 MB||12 MB||54 MB||40 MB||40 MB|
|RAM at 4 tabs||151 MB||335 MB||236 MB||395 MB||271 MB|
The best alternative web browser is Otter Browser with QtWebEngine (based on Chromium), made by a Polish developer Emdek. This is the only multi-process web browser out of them and has a really good performance. The second place goes to K-Meleon. That said, QtWebEngine is still in the works, so it may be buggy, and it uses more memory than Gecko engine used in K-Meleon.