For me it seems like any system with DDR4 conjures more frames when going past some FPS, but I can't do any tests myself before Taichi happens for Scandinavia. This is the only reason I have managed to come up from all these DDR4 speed tests showing either zero to steady increase.
What this would mean for some games is that lowering couple settings would get you past that magical line like 60FPS, DDR4 kicks in and you gain extra 15FPS.
Closest example, GTX 1080 & Ryzen 1700 @ 4.0GHz.
For that game it probably is 90FPS which is not realistically something I'd bother aiming for, and if I'm just wrong then these flat lines are even more bizarre.