iiiiim not sure how you were able to app and system data without being rooted
irregardless,even if you restored all app and system data,you have still cleaned out your caches by flashing this,wich is why your phone is smoother. GB by default is smarter and better at killing off unneeded background apps and process. maybe a combination of freshing up your caches and such,and a more dramatic affect of GB vs froyo on your particular device.
this update didnt feel particularly smooth or fast to me,but it might be because ive become spoiled by AOSP