node.js 4.0 released few days ago:
https://nodejs.org/en/blog/release/v4.0.0/
https://github.com/nodejs/node/releases/

node.js now migrated/merged with io.js and has new engine, features and may also have performance increase, see:

• NodeJS 4.0.0 is 8% faster – we tested it!
• What you need to know about Node.js 4.0.0

I just did a very very simple test use npm test on cdnjs/cdnjs

First with v0.12.7

peter@aws~/cdnjs $ node –version
v0.12.7

peter@aws~/cdnjs $ time npm test &> /dev/null
real 0m2.203s
user 0m2.193s
sys 0m0.101s

peter@aws~/cdnjs $ time npm test &> /dev/null
real 0m2.187s
user 0m2.143s
sys 0m0.129s

peter@aws~/cdnjs $ time npm test &> /dev/null
real 0m2.177s
user 0m2.129s
sys 0m0.139s

And come with v4.0.0

peter@aws~/cdnjs $ node –version
v4.0.0

peter@aws~/cdnjs $ time npm test &> /dev/null

real 0m2.395s
user 0m2.358s
sys 0m0.138s

peter@aws~/cdnjs $ time npm test &> /dev/null

real 0m2.403s
user 0m2.278s
sys 0m0.222s

peter@aws~/cdnjs $ time npm test &> /dev/null

real 0m2.395s
user 0m2.387s
sys 0m0.111s

Didn’t see the performance improvement in this test :)
(But I can’t say there is no performance improvement, this is not a benchmark)