It would be great to be able to specify a different extrusion multiplier per feature type. My main reason for requesting this would be to set a slightly higher rate for TOP solid layers than for outline shells, etc. On most of my printers any model sliced in S3D usually has perfect outline perimeter surfaces, but the top surface usually has gaps even if my calibration and infill are properly set. If I bump the extrusion rate up enough to make the top surfaces look good, I start getting artifacts associated with over-extrusion on my outline surfaces (zits, etc).