Wouldn‘t take OC if I were taking anything under D. I compared nearly all of them and the OC lost in smoothness with little to no improvement to the efficiency. From E onwards it’s a different story, but that won‘t be of any interest to you.
I like the more aggressive plates but get a very very smooth shave from the C plate. Looking at the chart below, I would guess that A or B in SB would be a good place to start your Karve journey.
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Edit: never heard this mentioned before but I really have the feeling that the brass Karve offers the smoother shaving experience when compared to it‘s stainless steel sibling.