So far, I had a good experience with PCI-E to PCI in Windows. It works. I installed different video, network and sound cards in 3.11*, NT3.51/4 & Win 95/98 on X470 motherboard with 2 PCI slots ( Asmedia bridge chip). As a bonus, this motherboard has some basic settings in BIOS for the PCI slots. You don't get this with an PCI-E to PCI adapter.
Letting aside sound cards... in DOS, I was surprised how easily you can install a NDIS DOS driver for an Intel Gigabit PCI-E gigabit card in Windows 3.11. (or 95/98) These DOS drivers are even up to date.
Now I want to buy an expansion box PCI-E to 4 x PCI. First I saw this model from Startech. But I guess this EX-1010 model (by Exsys) is 100% the same but with a 50% discount...
Did anyone tried one of these boxes? They are not cheap considering that with 20$ you can buy 1PCI-E to 2 x PCI. For 215.79 € you exchange one PCI-E 1x slot for 4 classic PCI, you get an elegant metal case and a solid cable connection. (I would never use one of those cheap PCI-E to PCI adapters with ribbon cables... )