Some folks will look at a 2-3 bottom moldboard plow, then compare it to a disc like what's shown in this thread and figure the disc will pull easily since it's not turning over the ground like the plow is, so they opt for a larger one.
Then they hook it up, set the gangs, and take off. And expand their knowledge base along the way.
Esshup, smaller discs like what you're looking for are easy to come by. I wouldn't buy new, as they show up regularly on implement lots, and farm auctions....fairly cheap. If you like, I will keep my eyes open.
