For single-threaded gaming performance, the X2 4400+ is going to give you about the same performance as a 4000+... Infact, the 4000+ may actually have just the ever-so-slightest edge.
Even so, I'd probably go with the X2. Since it is '400+' faster, the MHz difference makes up for its gaming short comings and puts it on par with the lesser 4000+ single core... But you get all the creamy benefits of dual threading elsewhere.