I don't understand the question. Is your title asking if you should use 100mm or 120mm hubs? It's based on your dropout width.
About the Shimano model, I haven't looked at the front hubs, but I did research on the rear hubs, which might be the same situation as the front hubs. For the rear hub, rs300,rs400, 5800 and 7000 seemed to be physically very similar from the exploded drawings except for lighter QR skewer assembly on the rs400, 5800 and 7000. Rs300 didn't show any polishing on the cups and cones in the specs. Rs400 does list polishing. Rs400 can be found really cheap. Looking at the assembly manual, rs300 and rs400 are probably identical except for the polishing. 5800 and r7000 are also probably identical, but they have a hex socket at the lock nut, instead of the traditional need of 2 cone wrenches on the rs300 and rs400. The 6800 and similar expensive models uses a dial lock washer that you can rotate around to set the preload on the bearings to prevent the cone from rotating as you tighten the lock nut. The specs say labyrinth seal so maybe slight better water shedding, and lighter aluminum axle.
Otherwise I think they all would perform very similarly.
https://productinfo.shimano.com/#/sp...m_Disc%20Brake)
Search the Shimano documents site for the exploded drawings and assembly instructions.