It’s all about the gain structure of your phono stage. The 1.2mV ART7 is fine at +76db on my Pass XP-25, but could get by with a bit less gain. The ART7 uses non-permeable coil formers, which reduces its output but provides theoretically improved SQ. In other respects the two cartridges are similar, and either should perform well on the 4PT. The ART7 is fairly high compliance. It sounds better on the 4PT with slightly lower inertial mass after removing the middle of its three main counterweights. I suspect that AT’s addition of the ART9 model was primarily about ease of use.