ASRock B650M Pro RS vs B850M Pro RS

[Duo]

I was planning a microATX build and was initially considering between these two motherboards. The B850M is seems better on paper but I was curious about one thing and was wondering if anybody could shed some light on the reason for it.

The B650M has 2 PCIe 16x slots but the B850M has 1 16x slot and 1 4x slot, does anybody know the reason for this reduction?

I'm planning to use it in a Lian Li A3 case. Any advice much appreciated.

 

[Duo]

I guess I wont likely need 16x for anything other than another GPU which isn't likely to happen anyway. I was more just curious as to what happened to the other lanes and if it meant gaining something elsewhere that I didn't know about from the specs I've seen.