CAD can often be very video card hungry, they make uber-powerful workstation cards for a reason. Since you didn't list a budget, I have no idea if this is feasible, but a dual Xeon rig with a Quadro 4 ...
SolveSpace is a free, open-source CAD tool that fits in 1MB, with a full 3D solver, parametric sketching, and a browser-based version.
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