Originally Posted by Sargas290X
It's a i5-2520M, a dual core but also a 35w part. It easily compares to some newer low power mobile i7's that are built to throttle. With a proper video card it could manage 1080p gaming, it could easily run games at the laptop's native 1366x768 resolution.
I actually just signed in to comment on this. You can indeed get an eGPU working on the T420, but the CPU will indeed bottleneck you to the extreme. I upgraded to an i7-2640, and used a P4CH express card adapter along with a GTX 770. After having to mess around with the OS's ACPI table, I was able to get the card to be hotswapped without a Device 12 error (which was a huge pain,) but the card really did not perform as well as I wanted.
The card did wind up using Optimus and enabling PCI-e compression, but there were so many situations where it would sit there either bottlenecked by the 1x PCI-e lane, or the CPU itself. Turns out HWMonitor has a bus monitoring option (and you can use task manager for the CPU,) and when the bus was not being saturated, the CPU was. This was using an external monitor, not streaming it back to the internal LCD.
I definitely think we are heading towards viable eGPU graphics, but this setup was not worth the hassle imo. I wound up just taking the card out and putting it into my server for folding.