Don't count on XMP with ECC UDIMMs

Probably not — XMP on ECC memory is hit or miss on that board.

Your ASUS X99-E WS is a workstation board that officially supports both registered and unbuffered ECC. But XMP is an overclocking feature, and ECC DIMMs are validated for stability at JEDEC speeds, not overclocked profiles. Some ECC UDIMMs do include XMP, but the board’s memory controller and BIOS treat ECC sticks more conservatively. You might get 3000 MHz to boot, but expect instability or outright failure to POST with XMP enabled.

You’ll almost certainly have to set voltage, frequency, and timings manually — and even then, 300