well, i'm not too knowledgeable about AMD (i'm more an Intel gamer, only had one AMD processor im 14 computers) but the difference is that MSI 870A-G54 exists, and MSI 870-G54 does not xD
There's a MSI 870S-G54
. The difference is that the A one has USB 3.0, and the S does only have USB 2.0 (the blue USB ports on the motherboard) and the price.
i still do not recommend any of them. Look at the big squares to the left of the processor socket, those are the chokes. those provide power to the processor. it STILL has the same 5 chokes (also called 4+1 design, since 4 are for the cpu and 1 for the memory controller). these are very bad for overclocking (the thread
i pointed you before has a more in-deep explanation, but if you don't understand it, i'd advise you to look at the horror stories, and look for pictures. I also didn't understand too much until i saw the pictures). There's another thread
of the "good" mobos for OCing AMD processors, because they have higher quality components, more phases, and cooling on chokes or mosfets. they might be more expensive, but i bet you don't want to fry your PC in under a year.