I finally found the reason why my high density infill parts had really rough, over-extruded looking top surfaces. Bambu Studio bridges over the infill on the layer before the top layers, and that bridging uses the regular bridging settings, which uses a very high flow. This is usually fine for low infill density parts as it can flow into the gaps between the infill lines and it will help build a foundation for the top layers. But, because I'm using a high density infill, the bridging flow is wayyyyy to much and there's nowhere for it to go but up and sideways. The infill bridging ends up having like a 0.4mm layer height worth of flow