v4. More efficient. RAM will be fine. I believe the ‘stock’ speed for DDR4 is 2133.

That’s something that I’ve never tried before.

I’m more so worried about performance loss having a SATA SSD mixed with an NVMe in parity. You’re talking a 500MB/s SATA SSD vs a 3000+ MB/s NVMe.

I have 2x 2658v4 in my Dell R730. Idle with no spinning rust, an old Quadro, and a couple NICs is ~120w.

I don’t know if I would combine NVMe and SATA SSD’s.
You need a boot drive as well, so one will be the boot drive, then 2 for the storage array (assuming you don’t boot from USB or something)

I personally would boot from the SATA SSD, then mirror the storage disks if redundancy was needed, or stripe if you don’t care for redundancy.

Possibility your RAID card was flashed to IT mode/with LSI firmware?

The RAID utility won’t work if it’s not running Dell firmware.

You can adapt the front DVD drive to a 2.5” SSD or you can use an NVMe drive WITH a USB drive with a bootloader on it (clover or rEFInd)

R710-30 do not have options to boot directly from NVMe, but you can use workarounds (like above)