His speed without teleporting is the same as any top level ninja. With Flying Raijin he even has a speed, its not instant. He says the clone would be
too slow which implies speed for Flying Raijin. Or else it wouldn't even be a problem to teleport the clone. There is probably a speed when he's moving through space and time that determines how fast he appears. He and Tobirama had to combine for the speed needed. It may be a chakra, or undead body thing, but it still has a speed when moving through space and time.
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See how Cooler and Goku are both using Instant Transmission in this 55 second video? They were both using it, but Cooler was able to move while between space and time at a speed faster than Goku, and catch him. Even when they were both using
Instant Transmission. So no matter what because of the Viz, Minato's Flying Raijin isn't instant.
[video=youtube;ysFbainm034]https://www.youtube.com/watch?v=ysFbainm034&feature=youtube_gdata_player[/video]
Minato is fast without teleporting, that much is true. A bunch of ninja are.