Diddy walking: 576
Dixie walking: 576 (DKC3), 512 (DKC2)
Kiddy walking: 512
Donkey walking: 512
Diddy running: 864
Dixie running: 768
Kiddy running: 768
Donkey running: 768
Dixie rolling: 1152
Kiddy rolling: 1152
Diddy rolling: 1152
Donkey rolling: 1024
The number is the amount of subpixels the character is moving every frame. There are 256 subpixels for each full pixel. So a speed of 768 would be 3 pixels.
It takes longer to reach topspeed in DKC3 compared to the other two games. I could go into more depth about their acceleration if you want
.
But yeah: Diddy, Dixie, Kiddy and Donkey in terms of speed.