it depends on your needs.
sandy e is about 40% faster
are you a composer? if so then Sandy E
just tracking mixing and not crazy stupid with plug ins then Ivy/sandy
if your Motu is PCI its not happening you have to do the trade in for PCIe regardless of platform
UAD 2 should be fine assuming you get the right mobo.
I run an i7 8320 on an ASRock X79 Extreme4 board and that still has two PCI slots. I have an old RME HDSP PCI and an very old UAD-1 PCI running and that works like a charm.
The Hammerfall runs well but I have a problem with the UAD-1. It would work but I’d have to reinstall the driver every time after boot to make the UAD-software recognize the card. I’m about to look after that at the weekend and see if this is a problem with the board, the driver or Win7.
But the RME is working fine in the PCI legacy slot.
Edit:
The UAD-1 now works (was a driver issue) and not only that, a second UAD-1 works with a PCI-to-PCIe adapter as well. I now have my RME HDSP and one UAD-1 working in the two PCI-slots and a second (PCI) UAD-1 running via an adapter in a PCIe slot as well.
I still don’t see any reason why to ditch PCI. It just works.