Just to reiterate my query, is there a flavor/effect that can be attributed to a particular profile (temperature vs time curve?
Convex curve tend to make the coffee taste something like...
Concave-straight curve make coffee taste more ...
Flat/straight curve tend to produce.... flavors.
Flat-convex curve will ....
Concave-convex (S) curve ...
Honestly, I don't think anyone here knows the answer to the above question. IF they claim they do, they most probably are completely FOS. And what might be true of one particular bean would likely not be true of others.
Given an "ideal roaster," one with lots of controllable heat generating capacity, well ventilated with a lot of control over the amount and timing of ventilation -- well, then you could probably test these ideas. But most real roasters aren't that finely controllable, and as a result, it is hard enough to try to get your roasts to "behave" to fit a few desired time/temperature parameters that testing these ideas on any one roaster would be damn near impossible.
If there is little appreciable difference between the pre-first crack profile (shape of the curve) I would tend to think that to achieve Ken's recommendation to slow down the roast prior to first crack than a straight-convex curve would be the easiest to "program" (if someone has such luxury).
Do not get me wrong. I will try all the above profile with varying time period for myself to find which I like most, if I taste a difference at all. That is, I will try to the limit of the frankenroaster that I will end up building.
Another factor is how much time one has to test every possible thing you can do to a roast profile. I certainly don't have the time for that, and there are so many other variables that it would be hard to ever be sure that differences you were tasting were the result of what you did with the roaster.
Still, it IS true that the beans that you use to make espresso, including whatever you did to them in the roasting process, will have hugely more impact on the drinks you make than with most any barista technique, or changes in equipment beyond a certain basic level.