I have 16GB of HyperX Impact 2133 MHz DDR3 RAM installed in my 17-inch Macbook Pro Late 2011 2.4 GHz running El Capitan (MacOS 10.11.6). I purchased the RAM on Amazon: Here Geekbench 4.0 shows an overall 5% increase in performance over the previously installed 16GB of 1600 MHz RAM. Some of the benchmarks improved by over 10%. Multi-core memory bandwidth increased over 27%!
However, there does appears to be some stability issues that have occurred since the install. I have been logged out in the middle of work (twice). PowerPoint has crashed (once). I had one crash using dual monitors. Also, GeekBench 4.0 has become unstable. My computer was running very stable prior to the install. I've had the 2133 MHz RAM in my rig for about a week and am still using it. I'll update this post if anything changes. I'm sticking with it a little longer mainly because I already have the RAM. I'm not sure the minor improvement in performance is worth the expense and reduction in stability. One more crash and I'm pulling the memory.
Another important thing to note is that Geekbench shows dramatic reductions in CPU performance when other applications are running (even when they are idle). So, if you're addicted to speed (like I am), you can achieve a much more significant performance boost by closing unused applications. This can give you an overall performance boost of over 20%.
I've attached a GeekBench comparison between my old 1600 MHz DDR3 and new 2133 MHz DDR3 RAM: