I think building an efficiently queryable set of all historic data is unrealistic without a separate cluster. We're talking 100GB/year, before indexing, which is about 400GB if we go back to 2008.
[etc]
So, these numbers were based on my incorrect assumption that the data I was looking at was daily, but it's actually hourly. So, I guess, multiply everything by 24, and then disregard some of what I said there?
-Ian