It all depends on who hones the razor.
I can get good shaves just like you & even a few Great shaves, the past year.

But,,,,,

There are members here who take the edge to a higher level,,, they put in the time studying the hones & how particular razors respond to the hone. They test & push different ideas for success or failure.

IMO,, it's not that you need that 12K, but will you put the time into learning the hone with the razors you have.

If your getting good shaves off the 8K,,, then I suspect you will see a slightly better edge from the start with the 12K,,, then the question, "Was it the 12K or are you good at honing?"

If your edges are good at 8K,, then your a good honer.