8B is not exactly great for roleplaying, if we put the bar any high. It is just not sophisticated enough, as it has very limited "reasoning"-like capabilities and can normally make sensible conclusions only about very basic things (like if it's raining, maybe character will get wet). It can and will hallucinate about stuff like inventories or rules - and it's not a context length thing. If there are multiple NPCs, things get worse, as they're starting to all mix up.

70B does significantly better in this regard. Nowhere close to perfection, but the frequency of WTFs about LLM's output are [subjectively] drastically lower.

Speed can be useful in RP if we'd run multiple LLM-based agents (like "plot", "goal checker", "inventory", "validation", "narrator") that function call each other to achieve some goal.