When he doesn't want to use them later, Sarda has a tendency to just warp someone away to a location they can't possibly return from. Like the moon, or a point "three seconds to the left of the future". Logia body isn't really going to help there...though it might let Kizaru actually return from the moon
As for Kizaru's speed, that's a more relevant issue. It really depends on whether or not Sarda actually has some sort of precog, and there's evidence for and against that in comic. For "against", we mainly have these three:
http://www.nuklearpower.com/2009/06/06/episode-1137-one-more-time/
http://www.nuklearpower.com/2009/06/09/episode-1138-use-your-words/
http://www.nuklearpower.com/2009/06/11/episode-1139-if-then/
The problem is that I'm quite sure there are several instances of Sarda knowing stuff ahead of time despite his younger self being nowhere in the vicinity. So even though his response sounds like a confirmation of RM's idea, it's likely that he still has some form of precog anyway. Still need to find actual examples for this though.
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Dying breath, light my blade and sing in shadow! Omega!