https://i.gyazo.com/9a9313c9018dc9fe47bf3ef6c1779ca3.png I have no idea. The only thing I know is that the different settings can be measured using a 1000FPS camera, and that the results indicate that v1 + fast sync has lower latency compared to v1 without fast sync or to v2, but it's still higher than RTSS. Overall: In-game limiter: good latency reduction. RTSS: small latency reduction. v1 + fast sync: no latency reduction. v2 or v1 without fastsync: latency increase. Anyway, this doesn't matter if RTSS is not an option (either due to preference or due to technical reasons.) In that case, v1 + fast sync gives the least latency. As to why, who knows. It just looks like a "hidden" switch from the outside. Due to the fast sync dependence however, it makes it a bad choice; it has stutter. So overall you're basically kinda screwed if you can't use RTSS.