I think even guesstimates are useless until at least beta. We have no clue for what kind of data SAFE will be used in practice. If it’s mostly used as a streaming/file-sharing (replacement for torrents/youtube/netflix) platform the average get/put ratio will be significantly higher than if it’s mostly used for cold storage.
Actually, if we could get some indicative numbers on how much digital data is stored world wide, and how much data is transferred per day over the internet world wide, then we could make a (very rough) guess.