Hi @chrisgonzalez,
ZBrush can perform well on relatively modest hardware as long as you understand what the limitations are. Even users with far more robust hardware can experience “lag” when working in a suboptimal fashion in the program. I just want to make sure that you don’t spend a lot of money on a new computer, only to find out the same issue is present.
The more points you have on screen at once, the slower navigational performance will be, especially if polyframe mode is enabled. This is why when a mesh has lower levels of subdivision, it will display those levels when navigating with the mesh to keep performance faster. If you’re working on a mesh at a single level of subdivision, there will be no lower levels to display, so performance will be slower from having to update all those points on screen at once. This will be true on any system to various degrees.
For users with more modest hardware, it can be useful then to avoid letting a mesh of a single subdivision level get too high in polycount. Better then to use the tools that require this to create a mesh of a moderate polycount that captures the necessary form, and then remesh it with ZRemesher or other to create a new , clean low poly base, and subdivide that base upward for the purpose of sculpting fine detail.
As far as a hardware recommendation, I can’t recommend anything specifically, only that the specs should meet or exceed the recommended specs listed on the following page for effective sculpting on higher polygon counts:
https://pixologic.com/zbrush/system/
Good luck!