Faster is better, right?
That’s 200mm/s raster engraving with LW4 and some optimized experimental server 
The machine is also experimental, built with 3 OpenBuilds 1m axis.
What control board are you using?
What do you think causes the edged to be heavier?
The board is a Cohesion3D Remix with actual edge Smoothieware.
Not sure what causes the darker edges, but I did not yet calibrate the laser driver and probably it’s also a bit fast for the cheap chinese driver.
I have the same problem on my k40 smoothie. Its like it spends too much time right on the edge.
That sounds like a problem with adaptive laser power adjusting during acelleration/decelleration, which smoothieware usually cares about.
Adaptive laser power assumes a linear response. I add a white margin to images to prevent acceleration in the image area.