How much? It's not a tiny amount that could only be seen in side by side testing, it can be a large amount, perhaps even as great as an order of magnitude in some situations.
Here's an example:
All three blades were sharpened wet at 18 DPS and were very close in hardness and each were driven through .150" steel wire (16D nail), twice. BTW, this test was repeated many times in different geometries, this picture wasn't a fluke.
The blade on the bottom was a high performing test standard (standards are critical). The blade in the middle was industry standard heat treat 3V. The blade on top was fully tweaked 3V with changes to the austenitizing temperature, quench speed and depth, the use of and timing of cryo and successfully avoiding the need for the SHH. Same alloy, same hardness, but perhaps about 1/10th the edge damage, just through a change in the heat treat. In my experience, the best heat treatment can make a huge difference that can easily be seen at an arms length.
note: I understand that hammering a knife through a nail a couple times is not a scientific experiment and stinks of hype. Please understand this picture is shown for the purpose of this discussion, and that particular test is only one of many and the test itself has been developed over time to look for particular characteristics that are hard to quantify. After a few boxes of nails the test becomes pretty consistent and predictive which are characteristics of a valid test, even if it looks a little retarded on the surface.
I have another great example of heat treat making an enormous difference in the performance of a steel. One of the things we manufacturer in my shop is an industrial Kevlar fiber cutter used processing the jackets around fiber optic cables in high volume production. Kevlar is hard to cut, the fibers are fine as silk and don't cut clean with a dull blade. I'd love to tell you folks all about it but there are things I'm not able to discuss here. But I can tell you this: steel had been a borderline material in a high volume application so they had been using carbide and getting 10,000-20,000 cuts. We looked at steel as a cost savings and the goal was 4,000 cuts, and when we started we were nowhere near that goal. After fully optimizing the heat treat for D2 we now get 250,000 cuts, an order of magnitude more than tungsten carbide. I know that sounds like insane bullshit, but I swear it's the truth.
Optimizing a heat treat is done like any other process optimization and industrial R&D. You control variables and set up meaningful experiments and then get to work. Those D2 Kevlar cutting blades are going to put my kids through college. :thumbup:
