Both, the two characteristics aren't mutually exclusive. Here are the characteristic curves, RMS granularity, and MTF resolution charts for Double-X from Kodak. The developer used to generate these data points is D-96. While I don't have an actual H&D curve plotted for it, I can pretty much tell by eye how it is when you print it. Note though that I developed the stuff in D-76 1+1 for about 7 minutes at 75F. Being a more aggressive developer than Kodak's recommended D-96, it's not surprising to see that the high end would shoulder off more quickly. Yet despite that the range through the middle displays less differentiated separation than you see with Tri-X.
