My x3i seems a bit sluggish and pauses alot in Auto mode. From what I read, there isn't a big problem with that unless you are playing games, which I don't.
dont use the dell performance utility.. it sucks cause it uses the 100mhz bus when in auto or powersave.. leave it at Full performance 400mhz at all times and use a 3rd party program like xcpuscalar to downclock your x3 and it also has a built in auto clock feature that is tons better than the x3 built in