I've been noticing this lately (with any video card) that in some games where i know i should be getting 144fps i may be getting 90-110. Both gpu and cpu are maybe at 50-60% usage.
Acer 144hz 1080p, MSI titanium 1070Ti (max temps 68c stock), 16gb corsair lpx ram 2400mhz, i5 7600k @ 4.8ghz (max temps 72c)