PCIe 4 as the reason to 'downgrade' the processor to the 2700x and overbuy the board to keep somewhere near a budget doesn't make sense to me.
If there becomes an all consuming need to go PCIe 4 on my main box at some stage the B450 board could have a Ryzen G CPU added to it and dropped into a second cheap box leaving the better processor/GPU to go into a 550 or 570 board.
Repeating this same upgrade exercise in a year might see a different conclusion as prices/tech moves around but currently it doesn't.
Sorry... I was looking at your stated budget. If you CAN pay the premium price for a 3900 Ryzen, GO FOR IT!
I wasn't suggesting to downgrade your CPU; I was suggesting the 2700X as I guessed it was the highest you could go and still have 16GB of reasonably fast DDR4 and a name-brand 570X MB.
CPUs ALWAYS come down in price; and sooner rather than later. They are by far a simpler and less painful upgrade than a MB swap for the features you WISH you'd sucked it up and paid for at the outset. But the price of a decent name-brand MB with a
full current-model feature-set has been $125-175 for decades now. Trying to come in under that is always a trade-off. I've learned the hard way that buying the cheapest MB that will support a CPU is penny-wise & pound foolish. You are ALWAYS giving up some current-model features, or a getting a board that simply is CHEAP or has effed-up BIOS that never gets fixed. (ASROCK, I'm LOOKING AT YOU
![Angry >:(](https://www.eevblog.com/forum/Smileys/default/xangry.gif.pagespeed.ic.0w4zhwjvDw.png)
)
Look at the MBs you're thinking of... and compare them to the feature-set of the 570. And remember that AMD is concurrently releasing a whole new family of GPUs that most likely will leverage pcie4.0 for multi-GPU processing. I just don't see the benefit of choosing a lesser MB that's going to be strangling your hot new CPU in some critical way; especially not to save $40-60.
But hey, it's your build.
Cheers,
mnem
*toddles off to fix another air compressor*