Tony (aarcuda) used the stainless on one of his small block engines, said they worked great.
He had photo's comparing the PRW and speedmaster arms, they looked identical in the pics and according to him (in his hand). pics and his experience is somewhere in the archives.
I'm using the PRW arms on one of my big blocks, so far so good. Had to correct the geometry as the underside of the arm was too close to the spring retainer.