Thinking about it: Not only can Kizaru deal with the attacks of Snakeman + FS, but he can also hit Luffy with FS. That man is decent to say the least.
And if Snakeman couldn't get the job done, Luffy might go for some G5 skills that somehow outspeed or generally outperform Snakeman. Really wanna what he's going to do.
How he's going to pull out more power, in case Boundman's power is not enough, is not difficult to imagine, but outperforming Snakeman creates room for a very interesting development, assuming G5's base speed is not already going to do just that.