I agree that there's not much to gain in multithreading. If you watch a process graph through a run, most of the runtime is at 1.0 or less. In-development versions will have considerable performance improvements without multithreading, though.

Here's our stats for the past 6mo of defacing jobs on our cluster:

11374  jobs between 20251029 and 20260429.
        MaxVMSize(GB)
Mean    6.23 
Median  5.46
p95     21.05 
p99     24.81  

However, these are running from source code (not deployed/compiled) and not containerized, so it may be different for you. We're running a variety of image types and the higher usages are typically full-dynamic PET with 40+ volumes. For typical images with 1-5 volumes, I'd say 10G seems reasonable.

I think you really want the png snapshots for QC purposes, but they definitely increase requirements and dependencies. 

Chris