Showing a new item immediately can make a product feel responsive, but the optimistic record needs a way to reconcile with the committed one. I prefer a stable client operation identity, an explicit pending state, and a clear treatment of conflicts.

Virtualization can reduce rendering work, but it changes how rows enter and leave the document. Before adding it, I would measure actual list size and check focus, selection, screen-reader navigation, and browser find. Sometimes a paginated list is the clearer product.