because of Specilized and their ability to apply a patent to a pivot point on the chain stay these were technically a faux bar linkage similar to kona at the time, the rear pivot being above the axle rather than beneath it. it technically a linkage driven single pivot as the axle is connected directly to the primary pivot point, this means the travel of the rear wheel wasn't linear like that of a horst link instead it arcs around the bottom pivot similar to a single pivot design.
what this means is that under braking you'll get more suspension compression and you get more pedal bob because you are directly affecting the rear wheel around a single pivot rather than the wheel and main pivot being isolated from each other.
truthfully none of this matters and they rode really well. it was one of the bikes I wanted back around 2000 as their was no way I could afford a horst linkage.
very nice bike and the 80mm Z5 is a great choice, they also did a 100mm version that would suit this frame very nicely if you can find a set. the Z5 might have been "budget" but it had technology that is still being used today unlike the higher end coil shocks of the era.