Partly agreed. I think the choice for a webserver / architecture is often taken not too well informed. And node is quite hyped, cowboy not. Who does not want to ride the waves of success? Netflix, airbnb, together with the big boys, all that applause, champagne, bubbles (!! 
etc! Benchmarks can help. I have not been seeking long, but here is an example (2011, quite old): http://www.ostinelli.net/a-comparison-between-misultin-mochiweb-cowboy-nodejs-and-tornadoweb/
But there are more parameters that are hard to measure.
