It's not that I feel it is faster. It is faster for me. No, it's not the serrations.
The flat plane on top of the 10-8 just works better for me.
I compete in IPSC. For some reason, the contoured top of the Warren just played tricks with my eyes. With the 10-8 rear, I can just quickly focus on the front sight, and get an accurate hit at any distance. With the Warren rear, I'm not exactly sure what my problem was; but I think my eyes were seeing more, so they would try to focus on more than just the front sight.
I'm sure the Warren is a great sight for many people. It's just not for me.
Ohhh, I'm using a Hi-Viz fiber optic front.