In one of the sections not shown here (temp at the bottom of an entry), there is a peak temperature that defaults to I think 70°C and then it goes to 100% anyway. The 100% if it reaches that warning temp , also adjustable.That is for the simple graphing.
But the real issue I see here is your Advanced graph is not good because "the software does not know what to DO after 50°C" So leave a wider range of temps on the graph, and give it a speed to be at at any of them. Have a range from 25°C - 80°C. You could also give a total range from ~20% (lowest speed the fans still kick in) to 100% based on 2 sets of sencors system and cpu, or even 3 to keep hard drives at nice cool temps.
It's a good thing that when the graph comes to the end of the user set speeds , that the speed would go to 100% because what if the heat was still going up , and there is no responce from the fans? The software is doing the right thing (unlike some other softwares :-)
As a side note , to me that graph is not taking advantage of the possibilities you have here at all anyway. Even if your fans would be loud and obnoxious when the temps are too high, that is one time it would be ok for them to be loud. Also if your temps are barely ambient temperatures there is no reason to overdo the ammount of air (and dust) being pushed or pulled through the case.
The Case Fans should be reacting more to the ambient or "system" temps in your graph, and can also have an added effect for when the cpu gets too high in temp . so the advanced graphing can be very complex and take much time to setup fully correct, but could also have your computer practically silent when doing nothing, and a hovercraft when working hard, to keep things cool. You can use multiple sencors for each fans graphing speed to achieve that.
Most peoples use of speedfan is not to lock to 1 speed, but to create a scenario where the best of everything happens at all tempertures, which I will admit takes a lot of time to get fully perfect.