Once again I need your help! I need to get the slice(index) of a spread defined by the smallest distance to another element. In other words: the index of the element of a spread which is closest to certain (fluctuating) coordinates.

check the “Former Index” output of the Sort node and take the last (or first) slice of it.

Points2Vector will give you the distance between two 2d points. when using spreads you can e.g. calculate the distance from any point to a given point.

is expr lame, should it be avoided with larger spreadcounds or am i
doing something wrong?

in theory expr should compile the math expression to some internal stucture once and just run through that for each slice. this should be quite fast, but is necessarily slower than the polar node, which is purely writen in delphi.