I defer to my colleagues who know much more about this, but the just-announced SWIFT cut-offs seem too small-bore to be a game-changer, but they represent progress.

This seems to be a well-informed thread:

One reason that it’s important for the Ukrainians to hold out is that the longer this fight goes on — and the more desperate and brutal the Russians get — the more pressure there will be on the West to stop holding back and apply truly punishing sanctions.