Decreasing the resolution does not have much effect as Xperia M is already running on a low resolution. I lowered it slightly, but I barely get any noticable increase.
Recently, Dragon Quest 8 has been ported to Android and I am using it as my Gaming Performance measurement.
It runs well and very playable, but it still lags now and then during sequences and I want to completely get rid of that. The graphics of the game look amazing (considering its a PS2 game on Android), but I'd be comfortable with smoother gameplay instead of great graphics.
I found some tweaks such as Medusa, but as mentioned my phone has a Locked BootLoader and it cannot be unlocked. I already disabled all animation effects in Developer Settings.