FYI, came in yesterdays update, means BC now adds a few extra % to rake back if you play a decent amount:

Black Card Improvements

Earn extra Full Tilt Points multipliers through your Black Card membership by reaching higher points thresholds. Achieve a 1,500-point rolling average to earn your 3x Full Tilt Point multiplier, or a 3,000-point rolling average to earn your 4x Full Tilt Point multiplier.


Apparently each extra level adds about 4-4.5% to RB, depending on playing style, which cash bonus you buy etc.