The only problem is that you need to maintain and enhance that MVP for the next several years -- unless it's just a hackathon.
I've spent way too much of my life trying to optimize Ruby performance and memory usage, switching from one web server to the next, then fixing threading issues in dependencies, and so on. It's not fun. All that upfront productivity is lost in the end.
Quite happy to spend more time upfront investing in a reliable end-product.