Your right about there been a point when you can go no further.

Steel can only go so far, And If you want to go higher then you have to start reducing the edge angle. At that point your edge has no strength and will disintegrate.

If you want a material that can go to ludicrous speed then you need to look into Obsidian.

Though not approved by the US Food and Drug Administration (FDA) for use on humans, obsidian is used by some surgeons for scalpel blades, as well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels, the cutting edge of the blade being only about 3 nanometers thick.[35] Even the sharpest metal knife has a jagged, irregular blade when viewed under a strong enough microscope; when examined even under an electron microscope an obsidian blade is still smooth and even.
Obsidian - Wikipedia, the free encyclopedia