I too used to love Konica Centuria Super for long exposures. Grainy but great reciprocity! At present Kodak only recommends you shoot Portra or Ektar up to 1s; after that they just say to "test".

Fuji Reala and 400H say use +1 for up to 16s but still don't recommend really long exposures, up to 64s for Reala.

I used to shoot really long exposures with E200 for astrophotos but haven't done that in a long time now. It was too red sensitive normally but good for astronomy in long exposures. Fujichromes were generally more cyan/blue sensitive at the time for longer exposures.