Both are good steel heat treats. I feel the heiji feels bitier and slightly chippier, but heiji also chips with a lower edge angle I feel. The shigefusa feels smoother upon sharpening and slightly easier to sharpen. They feel more similar than not. Having sharpened and owned carbon swedish heiji (1), shigefusa (2), iwasaki (5), they're all good. Iwasaki has the finest microstructure and is the hardest when sharpening. If you're after finest edge taking, well, razors are where it's at. But for kitchen knives whatever works, works. I have gotten used to being fine with bitier coarser things, as well as coarser grits (320, 400) for regular kitchen tasks, out of laziness but also seeing that it works fine with careful deburring and light sharpening pressure, and a cleaned stone.
Seriously though, I pondered the sharpness question quite a bit, you can certainly explore that route, as I have with various blacksmiths works via western, and a bunch of Japanese tool, razor, knife makers. Axe heat treat vs nata vs stone chisel vs kanna vs wood chisel vs tungsten carbide edge taking vs deba vs usuba vs yanagiba vs stainless etc etc. I've said a couple times that I really like tosa treat, and some softer stuff, for kitchen knives too, or even the sk type or basic carbon steels used in vintage Japanese forged monosteel carbon.
I will say that heiji leans a bit toward his saw background in edge bitiness bc for saws that's an essential trait.
Ultimate sharpness matters more for razors and even then, I also don't prefer diamond stropped ultimate sharp razors -- I feel they cut skin and leave it razor burned more for me. And for example, tamahagane, I didn't prefer iwasaki tamahagane, which many consider to be the pinnacle of pure steel. Not did I necessarily like much more vacuum remelt extra pure white steel (tried 2 kanna, kunio Yokohama, tsunesaburo), nor tamahagane kitchen knives, nor sc145 (raquin).
I'm can get the job done with vg-5, and molybdenum steel, and SK, etc
