Who is to say that you cant go beyond the speed of light in the dbz verse. I mean you have people who can destroy whole solar system with their life energy or ki. You also have people like goku who freely teleportation beyond the heavens and earth.Let's not get so technical here but since Goku is made of matter, he can't move at the speed of light or faster. Kizaru on the other hand is a different story.... so no
but yes, Goku is still stronger. Though I'm sure if Kizaru enters DBZ world he would be pretty fucking strong, since his limits set in his original world wouldn't (or shouldn't) apply to DBZ world. Kinda like how Batman is a lot stronger, smarter, faster when he's in the Justice League universe vs when he's on his own, against regular, non-superhuman villains.
If Kizrau enter the dbz world he would still have the same strength, sure he could train but he would reach the limit.