6430 vs. 6420 Performance Comaprison Under Heavy EMI...

Hats off to the design engineers behind the 6430 model Dell. Our company specs Dell computers coupled via USB to our specialized electric motor test equipment. This equipment is often subjected to heavy EMI from industrial variable frequency drives (VFD's). With the 6420 the mouse pad and sometimes even the keyboard would become unusable. However, the 6430 seems unaffected in the exact same environment.

Can someone tell me what changed to create this sudden stability. Can we expect it to exist in future models? Can I ask for it?