Aside from having to wait on a BIOS revision that supports that CPU, it should do relatively okay. Not ideal for overclocking. But the gains from the new CPU should be enough to make that worthwhile regardless.
The motherboard should work well with a 5600X CPU although it won't enable SAM to function with a 6800 GPU. But just how much performance uplift SAM gives in actual gaming we'll only know once reviewers have a chance to test it out. Also, with Nvidia launching their version that works with all CPU's on any motherboard it will be interesting to see if AMD continues to limit SAM to 500 series motherboards only.
Also, be aware it's going to be a while before a BIOS is available to run the CPU on 400 series motherboards. Early 2021 is what AMD says.
It won't just lose performance as the motherboard needs a BIOS that will recognize and initialize the CPU otherwise it will simply refuse to operate.
B550 motherboards came to market before BIOS' made for Ryzen 5000 processors were available. That's why you need to ask if it's 'Ryzen 5000 ready'.
B450 motherboards won't get a BIOS until sometime early in 2021...maybe January. But once they have a BIOS that works with it a 5600X should have full performance to the limits allowed. What that means is it won't support PCIe gen4 or SAM with a Radeon 6800 or 6800XT GPU, but that's also true with any Ryzen 3000 processor.