I have a Precision 3450 where the only PCIe Gen 4 capable expansion slots for NVMe storage is the NVMe slot closest to the CPU and the one PCIe x16 slot (with an adapter card). The other two NVMe slots and the PCIe x4 slot are all Gen 3.

I have a RAID1 mirror of NVMe drives where speed is important. I have found that I need to cannibalize the x16 slot for the second drive in my mirror, which ends up "wasting" three of the Gen 4x4 lanes because there is no PCIe bifurcation support in the BIOS.

I don't need whatever the latest Precision model is, but I would like to take advantage of all available Gen 4 lanes provided by my x16 slot for storage in my next upgrade, which will require BIOS support.

What is the oldest Precision that I can upgrade to that will provide this feature?

I am considering a PLX adapter that is capable of splitting the lanes on the adapter itself in the meantime, but I would like to know what my next upgrade path will be. I am only considering the SFF Precision models, not the desktop tower.