Yep GLH,there is no USDA grade of high in a category.
As you suggested,many of us look at an expensive steak and check for marbling,a vein of gristle running through it,etc.
The" branded" beef, like Certified Angus Beef, advertise that what you get will be from the top of the grading pyramid ,where prime is the very top and choice may go down another 10%-12%.
They" claim" to keep their shipments in the upper range of choice.
The Hereford programs have a similar program,that they give their own assurances without USDA grading.
Some high end markets may offer these and Prime.