I hate it when people change the question so they can give the answer they want to give, but I'm going to do it anyway, as I think its a relevant data point; I think you're dismissing the ability to run a database too quickly.

I have done almost exactly what you're talking about with a raspberry pi, using Ruby on Rails (3.0.x era) and sqlite. the Rasppi (model B) had enough horsepower to run in development mode on webrick and handle ~5 rps with page rendering and database calls, and that was in develop! when running in production, rails does less reloading of resources, so should be even more efficient.