I want to add a second 7900XTX, question about pcie2/3/4

I've got a 7900XTX in my old gaming PC, now I want more vram and if I stay on one GPU I can only reasonably get 32GB and that just doesn't sound good enough. Using two slots, 48GB sounds way better and is much cheaper. I think 48GB is the minimum I want to have after going to any effort and expense.

But I hesitate about the second GPU because the motherboard is a b450 with pcie 3, but only pcie 2 for the second GPU. I don't know how much this would hurt. I can see a lot of b550 motherboards come with pcie 4 with pcie 3 on the second, I don't know if this is worth springing for. The CPU (5800X3D) only has 24 pcie lanes, I don't know if that is even relevant here. I don't know a lot of things.

I've read that tensor parallel isn't well supported anyway for these GPUs, so I guess I end up layer splitting anyway and I hope this means I don't have to worry about it at all. True? Or is pcie2 still gonna be a problem?