Anything which is not stock AOSP will lag. Why? Too much bloatware inside.

I usually install CM11 or PA on all my Android devices after warranty. Take my HTC One M7. With 2GB RAM and Snapdragon 600 processor, it is kinda slow with Sense UI. After CM11, woo... really can fly. Now, I'm using Paranoid Android 4.5 BETA 5 on it. Stable and smooth.

Next on my upgrade will be the Sony Xperia Tablet Z. Stock Sony UI really sucks! Slow and lagging.

Antutu is not a real way of measuring daily performance. U can have a very high score but the stock UI still lags.

Waiting for Lollipop which will blow away iOS 8 into the toilet. Worse upgrade ever for iOS devices. All my iOS devices not running at optimum level since then. Apps crashed often and WiFi lagging. Worse part, I can't downgrade back to iOS 7!