Note: This post is specifically for model i9100 international.
Features like smart stay and smart pause are too interesting to use. Don’t be upset if you are still using Galaxy s2. You can use custom ROMS available to boost up your device speed and looks. There are tons of ROMS available in the market but the one nearest to be called look alike is ROMS4 ROM. This ROM inherits many features from Galaxy s3 and s4. If you like multitasking then this ROM is for you. It consists of undervolting feature that allows you to save battery in real time. There are some application glitches in this ROM but overall experience is great. This ROM implements Android 4.1.2 which is not as great as latest 4.2.2. So if you can handle this ROM give it a try and tell us your experience. Installation criteria will remain same as older post->
Rooting and installing Android Jelly Bean 4.2.2 on Samsung galaxy S2 i9100.
Click here to download this ROM
Sources: xda, galaxys2root