I don't rate Dell's at all really. They have some really good selling points (good processor, great storage), but I think the graphics card is a bit naff, and in terms of upgrading you have no where to go really. They are very tightly compacted together inside, so you can't really put anything exciting in there. Also, they cut it really fine with the PSU (460W last time I looked), just rules out putting a really meaty graphics card in there.

The Chillblast looks quite good, have you had a look at somewhere like PC Specialist or Scan?