According to the Fuji data sheets, the FP-100B resolves 25 lines/mm vs 20 lines/mm for FP-3000B.
It also has better reciprocity characteristics: no adjustments needed down to about 10s exposure time vs 1/10s for FP-3000B.
I'm not good at reading characteristic curves, so I can't figure out if it's lower contrast. I don't really see a difference.
I'm well stocked with FP-3000B but just picked up one pack of FP-100B at the Film Photography Project store during the short time they had it in stock. Will give it a try sometime this year.