It seems to me I have asked the wrong question. The term "roll rate" appears to relate to a stabilized process in which the initial inertia has been overcome.
In a plane like a B757 the wings are long, the engines are outboard and the fuel tanks go well out along the wings, so there would be a lot of inertia.
The proper question is not roll rate, but time for a roll of a specific number of degrees. Since flying at 2g is within the permitted range, which has a bank of 60 degrees, does anyone have a figure for the time to go from wings level to 60 degrees, with maximum control wheel input, in a B757?