So as someone who restores stoves and runs a gasket kit business on
Ebay, the best gasket for your stove is exactly what the manufacturer designed the stove with. This is what its tested with, and how it was designed to operate.
Many modern stoves use majority low density graphite coated gasket. Most all vintage stoves used high density gasket. Which used to be asbestos rope for awhile.
And even the hardware store stuff does not tell you what density it is. (Which was your question)
You cannot tell by just the color if its an hd or ld gasket. My manufacturer here in the usa , can make me any density rope or tape, white or graphite coated, stainless steel mesh, pressure adhesive, tadpole, literally anything. The biggest difference with the gray rope which has the graphite coating, is that it will last longer than plain non coated white rope. Other than that they are still all rated to the same 1000 degrees, and can be any density.
The problem is, some stove companies are pretty tight lipped about what gaskets exactly they use. Because they want you to keep coming back for their oem kits. Some will tell you size but not density. Which is only half the equation. It takes a lot of digging to get ahold of the real proper specs for some of these gaskets.