Lowering the details in Overwatch resulted in hitting the internal FPS cap of the game, so GPU load was reduced.Thanks for all the feedback. I can give you a little bit more information about the details of input lag.
We use only unadjusted raw input for our input handling (except when in the UI) as is common for FPS's. We also do a few other things to try to minimize input lag (sample input at the latest possible moment, minimize allowable buffered frames in the driver, etc).
However, we have noticed that if the GPU gets bogged down, input lag will be a little bit worse because the driver will start to buffer a frame and there can be a frame buffered in our game (we have a multi-threaded renderer that has a frame in submission to the GPU while we simulate the next frame). In those cases if you want to prefer less input lag over visual quality you can reduce your graphics detail settings to ensure you get the quickest path from sampled input to result on screen.
I think it's still beneficial to cap your frame rate even in games where you get high frame rates. At very high frame rates (400FPS and up) it doesn't make a difference. 1 frame at 400FPS is not worth mentioning. But 1 frame at 200FPS is somewhat significant. If your PC maxes out at less than 200FPS and even though your minimal FPS is still in that ballbark (160-ish for example), then a cap might actually improve input lag.