compare two (x,y) plots or vectors optimally

Question: What's a good and fast way to find out whether an (x,y) curve (gray in the figure) is above or below another (X,Y) curve, let's call it a "bound", (shown as red/purple, green, and orange in the figure)? The values of elements of x and X vectors are not the same though the span of X (the bound) cntains x (the curve). More details below.

Background: I have about 5000 (x,y) curves, similar to the gray curve in the figure, and per each gray curve, I have 4 possible bounds shown in orange, red, purple, and green in the figure. The set of 4 bounds are saved in files and there are aboout 800 such files. I'll create the 5000 (x,y) curves and compare each with a one of the files containing the 4 bound curves according to some logic. I'd like to see whether a curve has a point higher than the bounds or it's contained by the bound from above. The values of curve and bounds values on horizontal axis are not the same (x and X vector elements are different) though the span of X (the bound) contains x (the curve)

[Rik]

Can you show what you mean with example data?