I have found that frame caps become more erratic the higher the FPS target. (Overwatch and Nvidia)
Using RTSS with a FPS graph, per frame update, 0 FPS average and a 60fps range above and below target I have a few examples.
This is a 60FPS cap using Nvidia frame cap:

240FPS:

350FPS with a 70FPS range:

and this is a 350FPS cap with RTSS:

Now the issues with this are straight forward: inconsistent input latency and added latency to low latency V-sync.
Because the FPS cap seems to be more erratic the higher the target, I feel like this is something that should be addressed before it becomes unuseable.