Hi, First of all congrats on getting progressed to the VI stage at both firms. That is no easy feat amidst an increasingly competitive cohort of applicants. I did my Willkie VI on the 2nd of December and received an invitation to their Written Assessment on the 12th. What I believe made my VI stand out is firstly, not regurgitating what you wrote in your application but rather, using it as a foundation to build new answers to the questions outlined. It is also very strict on timing so I would recommend practicing answering commercial questions in 90 - 120 seconds where you have free time. There will be questions that throw you off/ you would not expect but use it as an opportunity to showcase your creativity and don't be scared to verbalise a viewpoint or idea that you wouldn't expect anyone else to know. Many times, this is seen as a strength rather than a flaw. Finally, it is imperative that you know the practices, culture and values of the firm as this underlies every question that they will ask you.
P.S Don't worry about stuttering or slight moments of hesitation - I had about 5 of these moments and they still progressed me onwards. Good luck!!