I don't know what your definition of a "very low" threshold is, but it's much lower than mine. If you're Uber or Amazon, Rails isn't going to work for you. But

I don't know what your definition of a "very low" threshold is, but it's much lower than mine. If you're Uber or Amazon, Rails isn't going to work for you. But that's fine because 99.9% of companies in existence don't fall into that category. I realize everyone wants to be the next <insert huge company here>, but the reality is a) you probably won't be; and b) given that you won't be, stuff like fixing poor caching strategies and inefficient queries are going to give you an order of magnitude more performance/buck than choosing <insert framework/language here> over Rails.