NVDIMMs can be much faster
There are two types of NVDIMM. One is a flash block-IO device using the DIMM memory bus, and the other is a DRAM memory with a flash backup on power failure.
The latter runs at DRAM speed, and can be directly addressed by register-memory instructions. That leaves FusionIO, and PCIe generally, in the dust, but using the capability needs some software changes.
So the speed argument only applies to the other type of NVDIMM, which is still tied to the storage software stack in the OS and the moving of 4KB blocks of data.