Since you said "my 1060 3gb," I'm assuming you already have it.

The easiest way to test this is to do so experimentally. Fortnite and Overwatch are not particularly heavy games, but 144 FPS is significantly harder to reach than 60, especially with a 3GB 1060 (I'm not worried about your CPU being a bottleneck). Try lowering the settings to the absolute minimum (perhaps with resolution down to 1600x900), then bump up the most intolerable settings gradually until your frame rate starts dipping too far below your target.