So a quick verification. The io is the difference between these two. The JVM is doing some caching somewhere, whereas the v8 engine is not. Making a small change to both (in order to ensure that both are using the exact same logic):

https://gist.github.com/2652991

and then I get the following results:

vert.x:

39890 Rate: count/sec: 3289.4736842105262 Average rate: 2958.1348708949613 42901 Rate: count/sec: 2656.924609764198 Average rate: 2936.994475653248 45952 Rate: count/sec: 3277.613897082924 Average rate: 2959.610027855153

node.js:

38439 Rate: count/sec: 4603.748766853009 Average rate: 4474.62212856734 41469 Rate: count/sec: 4620.4620462046205 Average rate: 4485.278159589091 44469 Rate: count/sec: 4666.666666666667 Average rate: 4497.515122894601

Making that change so they both store the file in memory and nodejs is 50% faster than vert.x.

This is using an m1.small instance on EC2, and both vert.x and nodejs only using a single core.