The core of my software rasterizer written for an Atari ST 3D game was trapezoids.* The polygons would be broken into trapezoids and then the fill was, what I thought at the time, fast dual DDA (for left and right edges) and then some fast memory fill for the parts that were word width between the two edges.

For your N64 experiment, you say there's no way to check if it's faster without an actual RSP implementation - was there something stopping you from doing so? I've seen other people write custom RSP code in present day.

* HP later patented this idea (expired now).