sudo nvram ResetNVRam=1
only removes the variables/entries marked for deletion, so "should" be safe and preferred to a deep NVRAM reset when you already flashed a never booted BootROM image previously. Even more so with a UEFI Windows install like yours in ambush, just waiting for the right moment to kill the NVRAM volume.
The thing is, this NVRAM variable that triggers the garbage collection was just discovered by
@Syncretic and we still don't know of any unwanted/adverse effects/failures that happen when you use it. The theory is very sound, let's see if any problems appear with a broad usage by MacPro5,1 users.
Making things abundantly clear here, deep NVRAM reset is preferred when you have a long running NVRAM volume since over the years there are lot's of valid orphans variables or even incorrectly formatted variables that still have the valid byte enabled, Windows UEFI SecureBoot data or even the NVIDIA web drivers blobs. Not your case.
Always use the correct tool for the job.