Managing Partner in Big Law vs. Global Group Head at a BB

The answer is Global Head at a BB. However, you're thinking about law compensation wrong. The Office Managing Partner doesn't necessarily get increased compensation for their role as the OMP. Often times they are still responsible for generating lots of billable hours, which is the primary driver of their compensation. In fact, the percentage of profits allocated to partners at a law firm is mostly tied to billable hours. Therefore the top earners at the law firms are the ones who are getting billable credit for the major relationships. They don't even have to directly work on the deals / matters. For example, if Bob the Corporate Lawyer owns the relationship with Public Company X, and Public Company X is involved in litigation which is handled by Mike the Litigation Lawyer, Bob would often times be credited for this revenue. Note there are some exceptions but this is largely the rule.