Default Why do AOSP-based roms have worse graphics performance?

I want to start this off by saying that I don't intend to bash any of the AOSP dev's around. They're doing a bloody great job.

With that out of the way, it seems like every AOSP-based rom i try (whether it's cm10.1, cm10.2, cm11 (3.0/3.4 kernel), miui, carbon etc etc just to name a few), gaming performance is way below Sense based roms. Is this because the Sense drivers are better optimized for Sensation? Is it a GPU tweak I've missed?

For example, on Sense roms I can play Temple Run 2 on Best Graphics and Asphalt 8: Airborne on Medium without any form of stuttering. On AOSP-based roms however, this turns into a slideshow. Have I missed something here? I'm desperate for some decent AOSP-GPU performance.

~Shadow
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Originally Posted by Android Pizza View Post
Fast and strong multitasking....? Did you recently get a brick in the head?
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Originally Posted by nightwalkerkg View Post
A phone is a phone, stop using it like it's a damn spaceship.
My weekly tech blog: shadowcodegaming.blogspot.com

Device:
Nexus 5: 16GB Black. Stock. Not rooted.