This is a very old post that seems to have gotten some recent interest.
Haybines with the sickle bar leave a very smooooooth surface. This is simple the result of what they are, one long cutting blade.
Discbine, no mater who makes them, height is determined mostly by the angle of the cutter bar. Since the cutter bar is made of idividual mower heads, as they are tilted forward, they leave what appears to be a scolloped surface. This is just they way they are. It will grow back fine, IF it is not cut too close for the specific crop.
Discbines are ment to run at a good ground speed. Go too slow and they do not work well. They need a good amount of material going through them to work well and not blow down the crop. Personally I have been running an old 5209 for about 10 years and get fine results. No the field is not as pretty as a haybine right after it is done. Yes it does miss a little here and there, usually where it is thinner. Couple tricks, normally keep the ground speed up. As long as you have the HP to turn it, you will not chock the machine. (In 10 years I have wrapped the bottom roller once in really really tall grass where I had slowed down going down a hill ) You want atleast 5 MPH or better. I normally cut around 7-8 MPH in most conditions as long as the field is smooth enough. With lighter crops like 3rd or later alfalfa, pick up ground speed a little and lower PTO speed ( go up a gear and drop engine RPM) especially down hill. Up hill and flat, hammer down again. Biggest problem I have seen, and had with mine was when I ran it too slow.