1) Max extrusion (extruder) speed setting in mm/s of filament. Preferably read from a table of speed vs. nozzle temp.
2) Speed setting for overhanging extrusions. When printing overhanging traces, slow down the speed so that extrusions stay attached at the beginning of the track.
I've been using MatterControl for about a year now making parts for my small business. In that time, I've come to appreciate good quality at the maximum speed. I've found that actual head movement is not generally an issue, and extrusion quality is the limiting factor. For most everything, I run the head at the maximum speed that the extruder is able to push filament. There isn't really a setting in MatterControl for this, but there is in my Repetier firmware. The problem is that if I modify nozzle temperature or nozzle diameter the max extrusion speed changes. The downside to this is there are other speed parameters that you may or may not want to be tied to the max extruder speed.
For the overhanging extrusions, I have a part with an internal ramp, and that ramp really needs support. But, if I turn on support, I get a LOT of support that I don't really need. Yes, support would solve this, but if overhangs are very high up the part, supports may fail. My part is about 11 inches tall. Additionally, I can slow down perimeter traces, but then my print times suffer. I want to run at max extrusion speed as much as possible.
Finally, is there a developers forum somewhere? I'm pretty sure something like this has been asked for before, and I'd rather do some reading and become informed rather than making a post such as this. For example, I would think that this is a Slicer issue, and perhaps I should be asking a question there.