Well, at First you have to decide how to play the game.
Mainly three ways are known:
1) Using all glitches
2) Not using any glitches
3) Not using any glitches but using ticking (is a sort of glitch)
the first one is a bad way to play.... in SG you had to run around the finish line and you can finish 3 lap in ten seconds...
see
http://neka.sakura.ne.jp/clip2.mpgNot using any glitches is a good way to play.
The main problem is that not all people (no japanese, for example) play in such way.
So you can't know which is really the WR and it's difficult to find vids.
Try to refer to Kartseven for that (sorry, i can't find his site now)
"Not using any glitches but using ticking" is the way i like to play the game.
I you dont know how ticking is done, just read here
http://mariokart.planets.gamespy.com/mksc/advancedstrategy.htmlNote that some tracks are glitch free (e.g. PC, BC1 and many others), and one track is glitch and ticking free: RR
Edit:
btw, which program do you plan to use?
I'm not sure that slowmotion is available in any GBA emulators, so you could take advantage only by using savestates.