I owned a D820 and used a D620 at work for a couple of years, and found myself preferring the 15.4" display of the D820. I had one with a 1920 x 1200 which was much nicer to work on than the 1280 x 800 display of the D620. I believe there was a 1440 x 900 option for the D620 which would have helped even things up. I had a T7200, 4GB RAM and a Crucial M225 in it towards the end of my ownership, and it felt more responsive than the QX6700 system I use thanks to the SSD. The D820 is the favourite of the many laptops I have owned and used over the years, and I only sold it as I needed the money at the time. The D620/630 are so similar to the D820/830 that it's pretty much a choice of screen size/resolution and weight.