Okay, so I'm completely new to speedrunning this game, haven't done a single run yet, but I would really like to get into speedrunning some kind of PC version. I've read multiple posts that tell you NOT to use steam version (which conveniently is the only one I have) because of slower loads and a slower framerate. If I understand correctly, the load thing isn't a big problem thanks to the timing system, but since experienced runners are still telling everyone not to use the steam version, I'll probably just have to accept that it's going to be significantly slower. But that makes me wonder: Why doesn't it have its own category if it's so clearly disadvantaged? I think this would make it way easier for newcomers like me since the steam version can be easily bought for a good price. If you want to (legally) obtain the disc version, you're at the mercy of the used market. And for me, I really don't want to pay money for a game I already own.

the game used to be timed in real time back in the day, where the Steam version was a much bigger disadvantage than it is now, so the framerate and loads argument is leftover from then and doesn't really matter anymore since we use in-game time now that avoids that issue.

The steam version still has small disadvantages, like extra menuing for changing the camera mode, which can be bothersome in a run where you need to do that a lot like in Sonic's story. Also as far as I know the controls are slightly worse on Steam, though I haven't played that version in years so I'm not sure exactly in what way. I assume the analog stick in less precise, but I don't know. This might be one of those cases where it's only a disadvantage when you're used to the other version but feels perfectly fine if Steam is the only version you know

I think the Steam version is just slightly clunkier than disc, but its probably fine to speedrun on and you're not gonna have a huge disadvantage anymore these days. If you do use Steam, remember though to setup the ingame-timer according to this guide: https://www.speedrun.com/sadx/guide/aryzs
Livesplit will tell you an autosplitter is available when you type in the game name into Edit Splits, but that only works if you play the disc version, so ignore that and set it up manually like in the guide