These 10" GRK are being driven through and into what? hardwood, softwood? I have noticed that driving T-30 GRK screws into soft wood is not a problem but when encountering hardwood there is a problem and a pilot hole is needed. After driven thousands of GRK I have only broken a few bits, 5-8 perhaps, and usually it happens when hitting a knot and a fresh battery. I do like the color coding provided by one maker, don't recall the maker. T-30= black.

You could try you local auto parts franchise, say Napa or Snap-On. These may be of a higher grade. These use 3/8 square drive and would fit the heavy duty Makita driver well.