I can only speak for my experience at the Assessment Day, and our group was quite small (15 graduates). My impression is that their high standards may be harder to deliver at some of the larger groups.
*Only 2 candidates were cut in my group (I think they weren't always thorough in articulating their opinions, so I think it was fair. Back up your answers with logical reasoning and examples, exuding enthusiasm and confidence, and you can't go wrong!)
The psychometric test was a bit confusing as some questions were repetitive so I felt I had to check back at previous answers to guarantee that I wasn't contradicting myself.