Dear Soby,
I am working with the latest release (FVP_Base_RevC-2xAEMvA_11.25_15_Linux64) and get very diverse numbers from realm VM experiment. As I mentioned earlier, I did not face any problem with the normal world VM. I tried and changed lots of configurations outside of FVP (e.g., pinning FVP process to a core or changing its command line parameters) and inside the FVP (e.g., disabling SVE for realm, changing realm RAM size, etc) but, still have unstable numbers in running a same experiment in realm VM. I think it it really worth to investigate this problem by your team or FVP team. I would be happy to share more details if it is helpful
Cheers, Sina