The video titled "Six Years of Ruby Performance: A History" presented by Noah Gibbs at RubyKaigi 2019 delves into the performance improvements of Ruby, particularly in relation to Rails applications. The talk emphasizes how Ruby has become significantly faster over the years, noting that Ruby 2.6.0 is approximately 172% the speed of Ruby 2.0.

Key Points Discussed:
- Performance Measurement: Gibbs highlights the importance of methodology in performance measurement, underscoring that measuring incorrectly can lead to misleading results. He stresses the necessity of a dependable benchmarking framework.
- Ruby Improvements: The speaker mentions that Ruby 2.6 shows notable performance enhancements, yet these improvements have not substantially translated to Rails applications, particularly without Just-In-Time (JIT) compilation.
- Benchmarking Rails: The Rails Ruby Bench was introduced as a tool to measure Ruby's speed specifically using Rails applications. Gibbs discusses the challenges faced in benchmarking real-world applications, including issues with compatibility across various Ruby versions and the complexity of large applications like Discourse.
- Concurrency Considerations: The presentation explores threading and process creation in Ruby applications, noting that enhancements in Ruby 2.6 do not greatly improve concurrent performance compared to Ruby 2.0.
- Rails Simpler Bench: Gibbs outlines a new simpler benchmark he is developing, aimed at providing more specific data on Rails performance without the overhead of other services like databases or caches.
- Hiatus from Benchmarks: He notes that real-world applications often obscure the advantages that Ruby's newer versions promise, making it difficult to isolate performance attributes.
- Future Directions: The talk concludes with Gibbs stating the potential for future gains if improvements can be made bypassing Ruby's Global Interpreter Lock (GIL) using implementations like JRuby or alternative threading models.

In summary, while Ruby's core performance has shown substantial growth, the benefits are less clear-cut in the context of Rails applications. Addressing how different Ruby versions impact performance within Rails requires meticulous benchmarking and consideration of concurrency mechanics. Gibbs encourages further exploration and experimentation within the Ruby community to harness these advancements more effectively.