The 800 is for stuff fresh from the flea market/Daiso (their knives are awesome and cheap) the 4000 is fine (for me) for daily showing veg and meat who’s boss. For straight razors I use 10k.
Regular use of a steel (daily for me because I have issues) means I only sharpen once a month. If you don’t, or you are using different steel in your knives you may want to sharpen more or less frequently.