Worth mentioning though that the highlighted figures (1.12 tok/s for OPT-175B for "FlexGen with Compression") are for inputs of 512 tokens and outputs of 32 tokens.
Since decoder-only transformer memory requirements scale with the square of sequence lengths, things would probably slow down significantly for very long sequences, which would be required for a back-and-forth conversation.
Still though, until reading this i had no idea that running such a model on-device was remotely feasible!