Interesting...so I wasn't imagining it!
I have a 1,000ft roll of Fuji Reala 500D that manifests this, although it's quite universally grainy. (It's ECN-2 movie stock which I can process). Maybe it's lost some speed - it must be quite old, although there doesn't seem to be much color shift (very little correction needed upon scanning, at least). I think my predecessor stored it well. Maybe I will try it at different speed settings and see if that significantly changes the grain aspects.
Also, with the Fuji NPS 160, I should probably try that at 125ASA or even 100 -- the grain overall was quite good, except in the shadows.