the t3400 is an older model with a 667 mhz bus
the t4200 is the newest of the 3 using a 45nm process but its power hog using 1.500-300v
the t5670 has 2mb cache double then what the other 2 have but its clocked a bit lower
the 5670 will win a bit if you multitask a lot
the t4200 will be good for intensive light threaded applications
t3400 isn't far behind the other 2 but it loses out to them