[bvk]

Just to elaborate on this, the CPU performance of the T420 should not be a concern. The T420 (and T430) use 35 watt processors, whereas modern ultrabooks use 15 watt processors. A T420 from 2012 can beat today's base model Macbook Air handily in CPU performance despite the technology upgrades in the past 5 years; it will just produce more heat doing it. And that's before the possibility of a quad core upgrade.

[stamps]

You're absolutely right about the performance.

The good thing about going to the T430 is because it has the later Intel Ivy Bridge (as opposed to the Sandy Bridge) processors. The Ivy Bridge / newer chip sets brought USB 3.0 with them. Even the i5 version of the T430 has two USB 3.0 ports.