I've been experimenting with enlarging and obviously 8x10 enlargements come out great but I was wondering to how big I could make a Delta 100 enlargement? And could I make an even bigger Delta 400 enlargement?

I know that the bigger you make an enlargement, the softer the image is. But I also know that the Delta brand was made to "close the gaps" when the silver reacts to light. So would Delta 400 be better for bigger enlargements than the 100? Because I also know that the smaller the ISO speed is, the finer the grain. Since the grain is more coarse in higher iso films, would that be better for enlargements? Like would that be less soft than lower film speeds?

simple version: 1) are higher film speeds better for big enlargements than lower film speeds? 2) How big can I enlarge Delta 100 35mm film ~or~ 120mm film vs Delta 400 35mm film ~or 120mm film