If your phone is slow I'd look at what software you've installed. I've only had my phone a few weeks but I find it VERY fast 90% if the time.
Auto task killer type apps I agree cause more problems then its worth. Haven't used one on this phone nor my previous Acer running froyo
Sent from my R800i using XDA App
LG Nexus 4 - Rooted, Unlocked 4.4 KitKat, stock with LTE Fix
Asus Nexus 7 - Rooted, Unlocked 4.4 KitKat, stock
Playbook (hey was free and makes a great XBMC remote!)
Acer Liquid E, Xperia PLAY, Acer Liquid E, Acer Liquid E (don't ask!), iPhone 3G, Treo 680, Treo 650, RAZR, some micro sized Nokia...