Have you tried Ultralite wheels too
I think thing with rota is is that they focus more on track racing wheels , so they have to keep under the 19 mark to keep rotation of the wheel close to the actual speed you are doing. Over 18 and the rotation takes longer, which makes your performance slower, perhaps only by a milli second but over a track race, say 5 laps could add up to over a couple of seconds. For better quickness 17's are recommended, but for looks 19's look fantastic, but 18's can look just as good if car is lowered.