Hard to guess whether ART 7 is trickle down or an improvement over AT50ANV. I have an ART 7. The bodies of both are aluminum and plastic. The main difference appears to be(from AT web site):
"This product(ART 7) keeps the basic design of non magnetic core MC type cartridge AT50ANV and changed the coil winding frame from a pure titanium armature to a newly developed liquid crystal polymer armature by an injection molding. This product also succeeds in reducing the weight of the vibration system compared to AT50ANV and provides the extremely natural and clear sound quality and ability to express three-dimensional sound fields inherent to non magnetic core types... Liquid crystal polymer used for the coil winding frame has not only an extreme mechanical strength but also an unique property which increases the mechanical strength as the product becomes thinner. Therefore it is the most suitable material for the vibration system of cartridges. This has high intensity and vibration absorption properties, enabling high-quality sound by suppressing unwanted vibration when from power generation."
"This product(ART 7) keeps the basic design of non magnetic core MC type cartridge AT50ANV and changed the coil winding frame from a pure titanium armature to a newly developed liquid crystal polymer armature by an injection molding. This product also succeeds in reducing the weight of the vibration system compared to AT50ANV and provides the extremely natural and clear sound quality and ability to express three-dimensional sound fields inherent to non magnetic core types... Liquid crystal polymer used for the coil winding frame has not only an extreme mechanical strength but also an unique property which increases the mechanical strength as the product becomes thinner. Therefore it is the most suitable material for the vibration system of cartridges. This has high intensity and vibration absorption properties, enabling high-quality sound by suppressing unwanted vibration when from power generation."