Without spoiling anything, the best level from a side story (imo) is on Hokkaido. You’ll have to work your way to it though.

I used to speedrun silent assassin suit only on Sapienza, that’s where I got a bunch of my hours in the game. I never beat any records or anything but I got pretty decent I’d like to think. I don’t remember my stats anymore though, that was years ago now.

OX used to be my favourite channel and is still up there, and I’d say their Hitman content is their peak. I’ve been watching them since their very early days when they were a small channel, and I’ve probably seen every video they’ve ever put out, and I’d still say Hitman is their best stuff. Definitely give it a watch.