Once I get a new PC I'll definitely try speedrunning this too.
I've thought up some categories and rules for speedrunning the game.
These are just suggestions, and are subject to chance once other glitches and strategies are found.
You guys don't have to use these. I'm just throwing them out there for fun. 
Although it would be nice to have some sort of system to go by like other speedrunners do. You guys can change these yourselves until something is found that everybody likes, if you want. Again, just suggestions.
Categories for Speedrunning:
-Any% Cheatless w/ Glitches:
Completing the game without completing all adventures or getting all coins/gems. Glitches are allowed. Using Ctrl+B is forbidden.
-Any% Glitchless w/ Cheats:
Completing the game without completing all adventures or getting all coins/gems. Using Ctrl+B is allowed. Glitches are forbidden.
-Any% w/ Cheats and Glitches:
Completing the game without completing all adventures or getting all coins/gems. Using glitches and Ctrl+B is allowed.
-Any% Cheatless and Glitchless:
Completing the game without completing all adventures or getting all coins/gems. Using glitches and Ctrl+B is forbidden.
100% Categories:
-100% Cheatless w/ Glitches
-100% Glitchless w/ Cheats
-100% w/ Cheats and Glitches
-100% Cheatless and Glitchless
These categories are the same as the ones above, except that you complete the game and complete all adventures and get all coins/gems/stars.
Rules:
-No using the cheat code.
-No using the MV.. But honestly, I'm not even sure about this rule. It's all about how you use it for it to be good or bad for speedrunning.
-For Any% runs, once the ending cutscene is activated, you can stop your timer.
-For 100% runs, the timer is stopped once every star, coin, and gem has been collected.
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Some things to note.. If you're going to use saving and loading, the speed of your computer effects the speed of which the game saves and loads. Especially when you have other things running in the background like a video recorder. Some computers can save and load faster than others, so be aware that it could be eating up your time. Same thing applies for loading levels and dialog files too.
If you need a timer, I recommend
WSplit. It's a very customizable timer that a lot of speedrunners use.