Well I have a Tomahawk and a Tomahawk max the only difference is the later has more bios space. They both perform exactly the same and both have been great boards. Me personally if you could find one of those new I would take on of them over an A520 in a heart beat. Honestly I truly believe they are the very best B450 boards that anyone made and a lot of reviewers agree. Definitely good VRM quality.
I am just not a fan of those bottom tier boards. The only positive is that it will likely get the bios update without hassle that will support Zen 3. The way I look at it though, is none of these boards will support Zen 4. It is very possible the socket will change but even if that stays the same the new boards by then will be DDR5 so still needing a new board.
So since you talked about wanting to move to Zen 4 then the newer board might or might not be a safer bet and yes the chances of bios maturity for Zen 3 will be much higher on a newer platform in general especially with B550 and 570. However historically that has not been the case on the budget boards. A320 boards didn't get by comparison get the updates and also didn't run the future processors well. These are budget boards with lesser quality parts. That is why they are cheap. So yah maybe that A320 supports Zen 3 but that doesn't mean it will run an 8 or even that 4600 you look forward to well. This is why I never think budget board are something you buy with the intention of expanding later. If all you want to do is what it did day one then by all means go for it.
Even with B450 boards many of them would not run 8 or more core Zen2 without some serious heat on the VRM's. MSi Tomahawk board however are exceptional her.
I would not do what you are talking about doing. If it were me I would get the b450 board if you can. Get a 3700x and don't worry about moving to Zen3. That chip is easily going to last for another year and a half and honestly probably more like 4 years of viability. So why spend more money to make 2 moves that in the end likely will still be slower than if you just did this now.
Then plan for that Zen 4 with likely PCIe 5 and DDR5 support that will really be a worthwhile upgrade in a couple years.
My B450 board has excellent OC control. I can run my at speeds that I believe will be competitive with what stock Zen 3 will bring to the table, of course that is a guess. Unless AMD really makes a huge leap in performance and surprises the world once again. Bottom line is that B450 paired with an 8 core Zen2 still has a lot of mileage left in the tank and I would not be scared of going that route if you so choose.
Right now MSI 450 Tom Max $115, and 3700x $274 = $389.00
Your plan Ryzen 3100. $115.00 + a520 Board $80 buck minimum. Add in a 4600 likely at the $250 price point. And you now spent $445 and still have a low end board and you have lived with much lesser performance do to MB choice alone, plus the much slower processor, to ultimately end up with a slower processor.
To me that makes no sense. Obviously if all you have to spend today is $205 then you gotta do what you gotta do. Just know also that processor is frankly too week to properly push the graphics cards now releasing and coming in near months. I think you will ultimately have a lot of buyers remorse.
On the last not it is very possible to that the B450 will end up running a Zen 3 chip just fine. And in the end maybe even up to a 12 core model. So in a couple years if that pans out you could have a really great upgrade path and that B450 would have served you incredibly well.
For those of us who bought them over a year ago they already have.
