My x220 with an i7, 16GB of RAM and a 500GB Samsung SSD. The thing flys. Just upgraded upgraded to the newest Debian release with zero issues. Everything just works.
Personally I'm OK with 1366x768, but my X220i is more of a travel buddy than a workstation.
For workstartion use, get a T420 or something with either the 1600x900 LCD or a swapped-in full HD panel.