Grain is a facet of the photographic process that I like to use. It’s akin to seeing the brushstrokes in a a painting I really don’t understand why photographic manufacturers and many photographers seem to be on an endless search for finer and finer grain structures
they are sunning shots, and the grain looks ace!
I've never shot HP5 on the basis of looking at on-line HP5 images and finding them too grainy for my personal taste.
If I really needed ISO400 for a situation where a tripod wasn't an option, and wanted fine grain, I'd use XP2. Of course this needs to be C41 processed but I do C41 processing for colour neg anyway.
If I could use a tripod, I'd choose either FP4+ or TMax 100, because I don't want obvious grain if I can avoid it. Both can be rated at 200 with appropriate processing adjustments - so rating HP5 at 200 wouldn't provide any benefit for my purposes.