(Above video is demo of CM12.1 using Note 4 but it is nearly identical for S5.)
For those of you looking for a good CM AOSP ROM (What is AOSP?) to run on your Galaxy S5, try the latest CM12.1 ROM builds by XDA user Albinoman887.
As of this post, official nightlies for CM12.1 ROM isn’t available for the Galaxy S5 but the next best thing is definitely these CM12.1 ROM builds. They are not based on the latest Android 5.1.1 like the official nightlies but they will give you most of the same features and based on Android 5.1. The only costmetic difference between the Android 5.1 and 5.1.1 versions are button menu, the Android 5.1 version does not have on-screen navigation option with your hardware keys off.
So far, I’ve tested the KLTE (for GSM Qualcomm S5 models) and the KLTESPR (for Sprint) and they both run flawless with everything working out of the box. With Lollipop, you will also have the ability to use your 4K camera just fine along with exFat support on microSD cards so you can use 64GB or 128GB microSD just fine. Performance is bad ass on these builds, I was able to score near 48K on Antutu with the stock kernel and no overclocking. Battery life is also the best I’ve seen, you will get plenty long battery life with these CM12.1 builds.