Showdown Rankings vs In Game Ladder

I always theory craft teams then build them on showdown and I won’t even start building in game until I hit the 1600/1650 mark just to be sure I’m happy with the team.

Are there any other benchmarks people go for? Or do people just build straight in game and test and adjust straight into SV?

Also I feel hitting decently high in Master Ball is so much easier than getting high on showdown; what would be the rough relation between showdown ELO and Game ladder?