Hi @louvfx ,
As @tobor8man says, ZBrush is almost entirely CPU-based. In most scenarios, the GPU is not a significant contributor to performance.
A beefier CPU can help here, but you’re still going to encounter performance walls. Sculptris creates new geometry in real time with the stroke, and the more geometry you ask it to create, the greater the performance burden.
It’s important to remember that the tools in ZBrush that only work at a single level of resolution with no subdivision levels are generally intended for the shaping of form, up to about a medium level of detail. If you’re encountering significant performance wall here, it’s likely you’re trying to work beyond the intended effective range of these tools. After a certain point it is expected that the artist will need to transition to a multi-resolution mesh in order to sculpt fine detail. A mesh in this form will be required to hit ZBrush’s full detail potential, as well as for best results when painting, posing, UV unwrapping, texture creation and export.
Good luck!