The point is, i think that in general there are sometimes big differences between certain LMP cars and others.
If you look http://www.mulsannescorner.com/aerodata ... s102i.html, for example, or http://www.mulsannescorner.com/aerodata ... cLMP2.html, you can already have a feeling about this.
I know this is a comparison between an LMP1 and an LMP2, but still the difference is huge and i know in other cases there is not such a big difference between certain LMPs1 and certain LMP2s. Anyway, basing on some other info i found, i guess that i was initially wrong and that LMP cars can have, at least potentially, more downforce than F1 cars.