Haven't tested this with the other variants, but the longer Speed I potion does absolutely nothing. I've compared it with walking, running, and flying without the potion, and it's no faster. It's possible it's just my slow RAM, but I thought I'd report it anyway, just in case it's not.
Comments 4
Can you reproduce it after restarting your Minecraft client?
If no, then what if you go to and from the nether? Does it stop working after that?
Did you teleport to other chunks before using the potion?