I've recently accepted an offer for McKinsey Sydney so I can give you a more recent assessment of the differences.
I'll breakdown my assessment into the Case interview and the PEI section.
The case interview differred in pace and content. Pace wise they moved quicker, didn't waste time on you rambling and will interrupt you more often. Be prepared of this, the key quote was "if it felt like I was moving quickly, it's because I felt you were doing well, so don't feel flustered as I interrupt and keep moving through the questions." The conversations are fast paced and you should feel ready to quickly outline your hypothesis and start spitballing with your Partner.
Content wise as you would know there is a large packet of case information available to the interviewers. My two Partner interviews barely touched the case information, in fact the Senior Partner just started talking in a very conversational manner, his exact words to begin the case. "Oh that's interesting, hey since you're interested in the services sector I've got this interesting problem that I hope you can help me with..." It was very fluid, the whole case lasted 15 minutes because it wasn't a structured Q1 Q2 structure.
I think the 2 key take aways from my interview experiences are that while real case practices are the gold standard, having the mental ‘muscle memory’ from talking out loud and being able to critically assess problems was also critical in my success. Furthermore being able to treat the interview as a friendly conversation helps in being more comfortable with the pacing.
Finally, the Personal Experience Interview were different in two ways, weighting and content. Firstly the PEI had more weighting than I expected during my interview rounds, especially the partner interviews. My preparation during first round for PEI was fairly light, writing down a few ‘head line stories’ on a notebook and hoping to be able to discuss the details as the interviewer asked. In reality the PEI section was literally 50% of your 60 minutes, going up to 60-70% in your partner interviews.
The feedback from my round 1 interviewers was that I should brush up on my stories to be more structured and detailed.
Secondly in the partner interviews they structured the questions differently, my final Senior Partner interview went like this:
"Talk about your leadership capabilities, but I want you to imagine you are on the front page of the newspaper, I want to see your 5 word Headline, and three dot points that are 10 words or less that described what you did."
They would ask questions such as “why did you choose to talk to X in this location?”, “what reactions were you looking for when you said that?” Unless you had really thought about your stories, these details would be hard to remember on the spot.
The key take away for the PEI section is that it is definitely a 1:1+ ratio for Case interviews to PEI, and your preparation should reflect this.
Good luck with your prep.