We generate graphs for huge datasets. We are talking 4096 samples per second, and 10 minutes per graph. A simple calculation makes for 4096 * 60 * 10 = 2457600 samples per lineg
Mark Bessey mentioned it, that you might lack the pixels to display the graph. But given your explanations, I assume you know what you are doing.
OpenGL has an orthogonal mode that has a z-coordinate inside (0;1). There is no perspective projection, the polygons you draw will be planar to the screen clipping area.
DirectX will have similar. On OpenGL, it's called gluOrtho2d().