Lightest, slimmest, fastest and most cut down ROM?

Can anyone advise what is the current lightest, and fastest ROM?

Coming from linux, it's pretty easy to pick a light weight distro, there are a tonne of very small but very fast options, with android it's much harder to tell what's light weight / fast, and what isn't.

I don't want to retire my S3, but it's getting a fair bit of lag on CM 11.2 (March release) 4.4.4.

What is the fastest rom/kernel for the S6?

Is the Note 5 rom for the S6 the fastest one? And what kernel would make the S6 have the best ram management etc?
Maybe if you guys have some benchmarks to compare, it would help :)