Kaidou could react to and block attacks from a Snakeman stronger than the one in WCI without Future Sight. I don’t think Kaidou can block his own Thunder Bagua without Future Sight—that tells us which attacks are faster.
Kaidou was able to react to and block a (stronger) Snakeman attack without using Future Sight (FS), but he was eventually overwhelmed by the barrage of strikes. This shows that Snakeman's attacks are fast, but not instantaneous to the point of being impossible to react to without FS.
On the other hand, Luffy had to use FS to avoid the Thunder Bagua (TB), which means that without this future prediction, he simply wouldn't have been able to react in time. This indicates that TB's speed is greater than that of Snakeman's attacks.