Accordng to the back of a pack of BHB7:
For those stringing BLACK 7 at mid-tension range with mid-range ground strokes, its power potential will be slightly higher than Big Hitter Silver, slightly less than Big Hitter Blue. Stiffness and control will feel slightly stronger than Big Hitter Blue and slightly less than Big Hitter Silver.
BHB7 is softer than BHS, so I'd expect it to be less durable. From my experience, BHB7 goes dead more quickly, but that might not matter for your client.
Silver 16 is probably a good first step to up the durability.