Considering the top layer/infill is technically an outer perimeter it should be linked to the "Outline Underspeed" setting. Or, make top layer speed separately configurable. Slic3r has a number of configurable speed settings perimeters, infill, etc which allow for fine configuring to get the best finish.
I've been using S3D for a while and this is one of my biggest gripes. I know I can set up a separate process for this but it should just be a setting. Having the top layer infill run at the full infill speed is detrimental to the finish quality.
This and some other issues have me continually returning to Slic3r, which I shouldn't find myself doing.