1600 --> 1866 will lower the rendering time, say, 10.00ms --> 9.50 ms (not that big). The same is true for 2133MHz, but it may or may not work stably depending on each APU / mb.
Nevertheless I recommend DDR3-2133 for future upgrade. For example, the upcoming A10-6800K, A10-6700, A8-6600K, A8-6500, A6-6400K Richland APU (March 19, 2013?
) all support DDR3-2133.
BTW A10-5800K supports madVR Level 4 for films just fine.
SD film: 19.5 ms
HD film: 22.5 ms
Full HD film: 13.8 ms
But it's not fast enough for videos.
SD video: 20.2 ms
HD progressive video: 23.2 ms
Full HD interlaced video: 18.0 ms
Full HD progressive video: 13.7 ms (only this works)
As you see there is a huge gap between the max allowed 16.7ms and the actual rendering time. DDR3-2133 won't help at all. I expect A10-6800K (20%-40% performance increase) supports videos under madVR Level 4 (with Chroma upscaling BC75+AR).
As for SVP, A10-5800K supports SVP Level 3g + madVR Level 3 with no problem (CPU and GPU usage < 75%).