I don't know much about these dells but I will say I have had great luck with the AMD's.
built a 6 core chip(the phenom black edition 2) with 8 gigs of ram on a gigabyte mobo.
I was never an AMD person always thought of them as Intel's little brother.
after a lot of testing I was blown away.
I have yet run in to any issues and anything where I would think my cpu could be better.
I do realize the i7's are great and a little better.im just sold on amd, it out perform's my second generation i5 using sonar.
I wish I could be more help with these specific models, im sorry.
are you going with a laptop because you need portability?
desktops are just so much easier to work on, because a good computer will last you years but sooner or later samething will need to be replaced.
best of luck on this, again wish I could help you more.