GO WITH THE DELL.... its quality sucks....
Yet, the toshiba's is even worse!! (somehow that is possible???)
anyways... you have to remeber that clock speed isnt everything....
the T4200 is faster as its bus speed is 800mhz, while the bus speed of the T3400 is only 667mhz....
bus speed is more important (to an extent) than clock speed....
I own the T3200 and it is COLD!!!
it does not heat up whatso ever!!!
but honestly... the heat goes up as the clock speed goes up!!
(in this case, theoretically the 3400 would be Hotter than the 4200)
but you wont feel a difference....
the temperature depends on the company itself!
I would go with the dell as it is better quality and it has a faster CPU!!!

also... i REALLY RECOMEND LENOVO!!!

lenovo.com/us/en