The terrain shouldn’t be ‘on your mind’, it should be discussed and agreed. “From this point until reporting point Z, MSA is X, so in the event of a depressurisation descent our initial MCP setting will be Y. Once we are on the way down we can then refine that”. Or similar so that whoever gets to initiate the descent has clarity.
It’s an interesting one to watch from the back of the sim as it’s so easy to rush, whereas once the masks are on and you’re talking to each other everything should be done in a measured and steady way. Almost always I ended up with “be slow and however slow you think you are it’s still not slow enough”.