Default Galaxy Nexus lagging immensely.

Hey guys. I borrowed my brother's old Galaxy Nexus while my HTC One is being repaired and I couldn't help noticing it lags. Immensely. I flashed SlimKat build 3 on it and before that I ran LiquidSmooth. I was under the impression that KitKat was supposed to be less resource hungry.

Is it because it's not "official" (from Google)? Would 4.3 run better, say in the form of CM10.2.1 stable?