40g IB at home is the new 10g, the mellanox 3 40g IB cards can be had for 50 bucks each off ebay.
6-8 years from now when the market is flooded with used 100g pcie4 intel cards and my current threadripper 3970x gets turned into the new ZFS server I'll be glad it has PCIE4 to make use of 100g over one of these:
Also of note, intel likes to hide that this 100g pcie4 card uses pcie4 since their platforms don't support it yet.
from the doc
pcie 3 and 4
HOST INTERFACE FEATURES PCI Express 3.0/4.0 x16, x8