Three points. 1. There's no absolute fixed difference between a curve and a slider, but to the pitcher, it will be about hand action. Classic distinction is turning the door knob for a slider, pulling the shade for a curve. But arm angle is also important. I haven't seen enough of Cingrani to know if his arm angle has been modified over the last year or so but if he's getting different action on his breaking ball, it may be that he has. Watching his two starts with the Reds on TV, I thought his arm angle was a bit lower in the first start than the second with the fastball and the breaking ball angle somewhat higher than the fastball in both (in other words, fastball and breaking ball angle more similar, less distinguishable to the hitters in the second start, which I thought distinctly better all around). But these are observations based on a very small sample size, to be sure.
2. If Cueto can come back, I think we need to be sure Cingrani continues to get innings--therefore back to Louisville. The only problem with this is that he has been so dominant there that there may not be that much for him to learn there.
3. On the question of his fastball and what it bodes for him. I say it's good. He's throwing very hard for a left handed starter.