Well, it is hard to say if the CPU is the bottleneck in Sparc based units or the memory. I have an NV+ on which I run several rsync backups pulling from an NVX. On average a share that backs up from NAS1 to NAS2 (both NVX units) that takes 30 seconds will take about 60 seconds going from NAS2 to NAS3 (my NV+). I have never been overly concerned on the time any of my rsync backups take since they generally happen I am asleep or in the background. NAS1 is my primary unit, and the NAS1 to NAS2 backups occur starting at 12:05AM. The NAS2 to NAS3 (again the NV+) start at 12:05PM, but since I am not normally using files on those machines, it doesn't affect me. The longest I ever remember a share taking to back up via rsync was about 15 minutes, but I had added about 50GB of video files to the share.
In any regards, I don't think it would be a significant difference with the increased memory, or Netgear would have done it long ago after the price of memory dropped. The one time I did have 1GB of ram in my NV+, I could not notice any file transfer difference. But that was in copy/paste to a PC, not NFS or rsync. I am extremely committed between now and next week, so I will try to time some controlled experiments next week to see what the impact actually is.
Remember - the NAS is not a backup plan.
Backup = Good, No Backup = Bad