I have LG Optimus 4X HD since 2012. It was good until I upgraded to JB 4.1.2 (official). Severe battery drain, game lags, heating etc forced me to install custom ROMs. First tried CM, better than stock but not as good as I wanted; then tried MIUI V5, much better than both stock & CM. Never tried custom kernels though. I even tried other Chinese ROMs (based on stock) to see if better. Battery, UI etc were more than satisfactory with MIUI but lags in games and sometimes hanging while opening apps were still frustrating. Then one day I saw "Performance Booster" somewhere & gave a try with free version first. It drastically changed the performance then I installed donate version which improved overall experience. As mentioned in the app it didn't improve benchmarks but improved phones performance for sure. In other words, it saved my money from buying a new phone. Now I don't need new one as I have 'Huawei Mediapad X1' for reading, games & watching videos, which I bought here in China for less than 300$ (it's 400 Euros outside China).