Gamers Nexus has a really good review up of the new value R3 lineup.
The AMD Ryzen 3 3300X does actually offer a significant advantage over the R3 3100 in gaming and some production applications, like code compile, when both are at the same frequency. As stated earlier, this is contrary to typical AMD findings whereupon an X-SKU (3600X) and non-X SKU (3600) part can be made equally, nullifying any value of the $50 letter suffix if willing to overclock. That's because the CCX layout, stated amply by now, and the latency hit incurred from the 2+2 3100 configuration.
In this regard, we actually suspect that the R3 3100 will be a short-lived CPU, or one which is minimally somewhat buried by other options. The 3300X is good and competitive, and until the Intel 10 series, AMD is only competing with its own rarely available R5 1600 AF and, to a much lesser degree, its 3600. The 3600 is a worthy upgrade for people who are going to leverage the extra threads in non-gaming applications, but we really are at a point where it's safe to say that an R3 is enough for gaming. The 3300X holds it together well for a $120 part. This isn't our go-to, but for people with a stricter budget, we are confident in its recommendation. The 3100 is hard to buy given the "it's only $20 more" mentality that PC builders often have, but if the 3300X really is out of budget, the 3100 isn't horrible -- it's just disappointing in the face of the 1600 AF, which is objectively better almost universally and technically cheaper at $85. It's also a unicorn, has an invisibility cloak, and is never available, so you're relying on luck to be able to get one. AMD is still making and selling the 1600 AF to retailers, but they are beeing scooped-up by scalpers and sold at ridiculous prices. That leaves us with the 3300X and 3100.
It's weird. It's like reviewing the 7700K again, except the price and the company are both flipped upside down. We don't really have any Intel parts worth comparing to, so you're looking at AMD up-and-down the product stack until hitting the 9700K and 9900K. We'll see what the 10-series does.