The system we used to test was an ASRock X99 Extreme 6 motherboard with a 6800K CPU and a GTX 1060 under the hood.
We started with 8Gig of Single Channel 2133Mhz and worked our way up using PassMark Performance Test 8.0 which should give us a general overall performance benchmark of the system.
8 Gig Single Channel DDR4 2133 MHZ
16 Gig DUAL Channel DDR4 2133 MHZ
16 Gig DUAL Channel DDR4 2400 MHZ
32 Gig QUAD Channel DDR4 2400 MHZ
While we can definately see an increase in performance, the increases aren't quite what most people would expect.
The biggest increase in performance was from 8 Gig Single channel to 16 Gig Dual channel which was an increase of just over 7%, but after that the increases were only marginal.