I've never seen those grades 1-5. For me the quality is assured by choosing beans from reliable roaster that ive bought from before.
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Your roaster is probably hiding the grade. It is a common standard coffee measure for growers, impex, distributers and wholesalers etc.
Not a roaster but it's my understanding that it's pretty easy to mis-roast a good bean to make it taste bad, but I haven't heard many stories about roasting a lower quality bean lot into something amazing.
I would think as a home roaster you'd focus your efforts on the best possible beans, but if you can take a lower quality lot and make it taste great, more power to you. I'm not going to turn my nose up at something if it comes out wonderful in the cup.
You didn't answer the question. No mention of roast. It's Cup profile vs grade. My contention is profile is critical and grade isn't very important as long as you screen your beans for duds and rocks.