In my experience, it's pretty rare for a project of this maturity to continue to get faster and leaner--usually you see more features and bloat bringing performance decreases. Somehow SQLAlchemy has managed to not only add features, but get faster and more efficient (even if these profiles do exaggerate its improvement over time.) It's an excellent project.
Just as we have compilers for programming languages the same now applies to databases queries and database abstractions, for better or worse. Hopefully SQLAlchemy's speed trend will continue and merely by upgrading to the next version your site can become faster.<p>Having used both relational databases and SQLAlchemy recently in production on an Alexa 500 website I'm quietly reminded that for the vast majority of applications relational is still a good match, especially with tools like this that can remove so much of the database overhead.