At what point the inner width is too much? 23mm is what my gravel bike gets, I'd be afraid of damaging the sidewalls on a 25c tire. Maybe there's finally a reason for tubeless road.
You're in experimental, but probably not yet dangerous, territory when the inner rim width exceeds about 75% of the true (not nominal) tyre width. You can get away with more at the back than at the front, because the front leans more.
gp5000 25c would become 29mm wide and gp5000 28c about 31mm, so a great match with the rim shape:
28c Vittoria Corsa G+ :
I have not tried them myself (yet), but people seem to be happy with them.