Considering your objective of applying to the M7 business schools (Harvard, Stanford, Wharton, etc.), you should make sure your application is as great as it can be. Below is a summary of the factors to take into account for each choice:
Option A: Taking the GMAT Focus
Pros: A 795-805 could raise the bar and improve your application.
Cons: laborious and unlikely to yield a score greater than your 780.
Option B: Waiting an Additional Year to Apply
Pros: A first-class degree from an institution ranked in the top 100 enhances one's academic standing.
More work experience improves your application, especially if it was gained overseas.
Cons: Adds a year to the commencement of your MBA.
Option C: Applying Next Year with HSE Diploma and 780 GMAT
Pros: 780 is already a good score, so get started on your MBA sooner.
Cons: The HSE 3.0 GPA could be a serious disadvantage.
Recommendation:
Combine Option A and B:
Take the GMAT Focus: Attempting this can potentially increase your score.
Wait an Additional Year:
Apply with a first-class diploma from a top 100 university.
Gain valuable work experience, especially abroad.
By maximizing your advantages and minimizing your disadvantages, this approach makes you a competitive applicant to M7 schools.