The reason why I am recommending Validus ROM isn’t just because this ROM is awesome, it’s also because it’s one of the best AOSP ROMs I’ve tried on many of my other Android smartphones (and trust me, I have more Android devices than most). It’s still not perfect by any means but if you want to maximize the performance of your aged T-Mobile Galaxy S2 and also customize the hell out of it, I don’t think there’s actually a better ROM.
For customization, you will find a LOAD of options including full ability to customize your status bar, notification drawer, lock screen, enable weather in status bar, customize buttons (short-press/long-press/double-press), enable soft keys, and much much more. For detailed overview, see my video above as I go through many of them. For camera, I recommend you to install Google Camera app from the Play Store, which will give you additional features like Photo Sphere, Lens Blur, and Panorama.