I did a little research a while back on sugars in roasted coffee. I found out shortly thereafter that others had already done this research quite thoroughly but it was largely ignored by our coffee community. Still, for a small amount of time invested and a little money invested in Benedict's Solution, you can easily determine for yourself where and when measurable sugars disappear in your own roasts and begin again in that search for peak sweetness with more knowledge.
You are wondering what I mean by disappear?
So you are thinking what makes coffee sweet?
Then you are thinking, is roasted coffee actually sweet?
That's the tricky part. All green coffee has sugar but not all roasted coffees have easily measurable amounts of sugar(I was only measuring reducing sugars anyway.) Some times in roasted coffees we taste sweet because the coffees do have measurable sugar content (a lot rarer than you think). A lot of the time it is simply a combination of chemicals that gives us the 'perception of sweet'. According to Coffee Flavor Chemistry, there are a multitude of chemicals in coffee that create a sweet or ethereal like sweet perception on the palate. So sweet isn't likely from sugars but sometimes it may be...
You can see where I began to have one of those turning points again.
It was our early cupping notes that led us to believe that fruity coffees were perceived as sweeter and that chocolate heavy roast coffees were not 'sweet' simply because the roast obscured that perception. We thought that the bitters of these darker roasts were obscuring the perception of sweet rather than it being a case where there were no actual sugars present in the darker roast. We did not know there was any possibility of measurable sugar in roasted coffee at the time. We turned a corner when we discovered this new layer of complexity.
I entirely re-thought my use of the term sweet and have been trying to establish what it really means now. I'm still working on it. The results were just one more thing that made me reconsider the whole running conversation on coffee.
When I did my research, I found something quite interesting. You can still measure sugar content in a rare few roasts, but as they get darker in roast, there is a point where no more sugar is easily measurable for each specific coffee.
Some green are much sweeter than others, but that would take a lot of research to really define so we must rely on our observation and what is commonly held as facts about different processing methods. Simply the fact that some coffees which should have more sugar content because of their processing method would be darker roasted to cover the defects of that same processing leave the entire picture very muddy.
The simple answer is 'there is no simple answer in coffee and be wary of those who offer them!'
In fact, the sweetest coffee I measured was the production roast of Terroir's Kenya Mamuto(a big reason in not offering detailed results publicly). Not exactly a chocolate and caramel coffee, Mamuto's a medium roasted fruit heavy coffee. I found that my results were tied to one roast profile and therefore only pertinent to that profile from that roaster. A radically different roast profile, even to the same visible color may yield much different results. The processing methods (obviously) seemed the key to sweetness paired with the level of roast. This is to say, there is no magic point I can refer to and say there, that's the point you killed the coffee or likewise, that's where it's always going to have the most sugar.
What does all that mean? I am still pondering it and I have little to offer but more questions. I encourage everyone to do the research themselves and find that point in the roast where the sugars die and correlate that to something in the cupping notes. Don't take my word for it, invest your time and effort into it and find your solution for your own roast style.
The topic is too overwhelming and requires too much investment for me to give one size fits all answers.
I would suggest this however...
Moderation, don't over roast it, and always be willing to scrap the profile and to look for something new and different... especially when the coffee is good enough!
Always do the research and don't just take some one's word for it. There is plenty more to coffee than what we see on the surface. Whether it be that nifty black light for sorting green or a little Benedict's for sugar research, do your own research on everything and you may find something amazing all your own.