I've never tried, but I thought screen tearing could only get worse with high frame rate. In fact, I'm not convinced at all by the idea that Gsync is for making 40 fps bearable. To me, Gsync is supposed to improve the experience of games that keep moving from 55 to 100 fps, therefore causing endless tearing, plus stuttering for the 50-60fps bracket.
I might reinstall Bioshock Infinite to see that for myself.
I am in the process of replaying Bioshock Infinite in all its 100fps gsync glory. Love it!